IEC 61249-6-3:2023

Materials for printed boards and other interconnecting structures – Part 6-3: Sectional specification set for reinforcement materials - Specification for finished fabric woven from “E” glass for printed boards

IEC 61249-6-3:2023 covers finished fabrics woven from ‘‘E’’ glass electrical grade glass fibre yarns that are intended as a reinforcing material in laminated plastics for electrical and electronic use. All fabrics covered by this specification are plain weave.
This specification determines the nomenclature, definitions, general and chemical requirements for the glass, and physical requirements for finished woven glass fibre fabrics.
Annex A of this document provides a style designator for each finished fabric glass style, with specifications on yarn, fabric count, thickness and weight in both SI and US system.
This standard cancels and replaces IEC/PAS 61249-6-3 published in 2011. This edition constitutes a technical revision.

Matériaux pour circuits imprimés et autres structures d’interconnexion - Partie 6-3 : Ensemble de spécifications intermédiaires pour matériaux de renfort - Spécification des tissus finis en verre "E" pour circuits imprimés

L'IEC 61249-6-3:2023 couvre les tissus finis fabriqués à partir de fils de fibre de verre de qualité électrique (verre "E"), qui sont destinés à servir de matériau de renfort dans les plastiques stratifiés à usage électrique et électronique. Tous les tissus couverts par cette spécification sont en armure toile.
Cette spécification détermine la nomenclature, les définitions, les exigences générales et chimiques relatives au verre, ainsi que les exigences physiques des tissus finis en fibre de verre.
L’Annex A du présent document fournit un identifiant pour chaque modèle de verre pour tissu fini, ainsi que les spécifications de fil, de contexture de tissu, d’épaisseur et de poids dans les deux systèmes de mesure, le Système international (SI) et les unités de mesure américaines (système US).
Cette première édition annule et remplace l’IEC/PAS 61249-6-3 parue en 2011. Cette édition constitue une révision technique.

General Information

• Status: Published
• Publication Date: 13-Jun-2023
• ICS: 31.180 - Printed circuits and boards
• Technical Committee: TC 91 - Electronics assembly technology
• Drafting Committee: WG 4 - TC 91/WG 4
• Current Stage: PPUB - Publication issued
• Start Date: 14-Jun-2023
• Completion Date: 04-Jul-2023

Relations

• Revises: IEC PAS 61249-6-3:2011 - Specification for finished fabric woven from "E" glass for printed boards
• Effective Date: 05-Sep-2023

Overview

The IEC 61249-6-3:2023 standard is an international specification developed by the International Electrotechnical Commission (IEC). It focuses on finished fabrics woven from "E" glass electrical grade glass fiber yarns intended for reinforcing laminated plastics used in printed boards and other interconnecting electrical structures. This standard serves as a key guideline for manufacturers and engineers working with reinforcement materials in electronics assembly, ensuring consistent quality and performance in the application of glass fiber fabrics in electrical and electronic laminated plastics.

As a technical revision of the earlier IEC/PAS 61249-6-3 (2011), the 2023 edition introduces updates for better alignment with current manufacturing practices and international quality requirements. The standard specifically covers the nomenclature, definitions, general and chemical requirements for "E" glass, and the physical parameters that finished woven glass fibre fabrics must meet. A notable feature of this specification is Annex A, which details style designators and specifications such as yarn, fabric count, thickness, and weight in both SI and US units.

Key Topics

• Materials Covered: This specification applies exclusively to finished plain weave fabrics made from electrical grade "E" glass fiber yarns used in laminated plastics for electronic and electrical applications.
• Physical Requirements: Includes fabric count, weave type, fabric thickness, fabric weight, length, width, filament diameter, and feather length. These parameters ensure the fabric’s suitability for reinforcement purposes.
• Chemical Requirements: Defines the chemical criteria for the "E" glass used to maintain electrical performance and durability.
• Electrical Properties: Sets dielectric constant and dissipation factor criteria essential to the reinforcing fabrics’ performance in printed board applications.
• Workmanship and Quality Control: Encompasses standards for splices, machining performance (including laser machinability), and acceptable defect classification to guarantee high quality production.
• Quality Assurance: Details statistical process control (SPC), inspection responsibilities, test methods, and sampling plans to maintain consistency and compliance.
• Packaging and Delivery: Specifies preservation, packaging techniques, and marking requirements to safeguard the fabric during storage and transit.
• Style Designators: Annex A provides a comprehensive style designator chart, facilitating clear communication of fabric characteristics, important for procurement and manufacturing processes.

Applications

IEC 61249-6-3:2023 plays a critical role in the manufacturing and quality assurance of reinforcement materials used in:

• Printed Circuit Boards (PCBs): Enhances mechanical strength and electrical insulation in multilayer printed boards.
• Electronic Interconnecting Structures: Supports the integrity and performance of laminate substrates in various electronic assemblies.
• Electrical Laminated Plastics: Ensures consistent reinforcement fabric specifications for reliable use in electrical insulation applications.
• High-Performance Electronic Devices: Assists in material selection for electronic components requiring optimal electrical and mechanical properties.

By adopting this standard, manufacturers can achieve superior product reliability, reduce material variability, and streamline compliance with international requirements for glass-fiber reinforced laminates.

Related Standards

• IEC 61249 Series: Covers a broader range of materials for printed boards and interconnecting structures, offering sectional specifications for different reinforcement materials.
• ISO/IEC Directives: Provides the framework for standard development, ensuring harmonization and global acceptance.
• IEC Technical Committee 91 publications: Offers additional standards related to electronics assembly technology.
• Other related standards in glass fiber materials and electrical insulation materials, which complement the scope of IEC 61249-6-3 by addressing the broader context of materials for printed electronics and interconnections.

---

Keywords: IEC 61249-6-3, "E" glass fabric, electrical grade glass fiber, printed board materials, reinforcement materials, laminated plastics, plain weave fabric, dielectric constant, dissipation factor, quality assurance, electronic interconnecting structures, PCB reinforcement fabrics, IEC standards.

Standards Content (Sample)

IEC 61249-6-3 ®
Edition 1.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Materials for printed boards and other interconnecting structures –
Part 6-3: Sectional specification set for reinforcement materials – Specification
for finished fabric woven from "E" glass for printed boards

Matériaux pour circuits imprimés et autres structures d’interconnexion –
Partie 6-3: Ensemble de spécifications intermédiaires pour matériaux de renfort
– Spécification des tissus finis en verre "E" pour circuits imprimés

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IEC 61249-6-3 ®
Edition 1.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Materials for printed boards and other interconnecting structures –

Part 6-3: Sectional specification set for reinforcement materials – Specification

for finished fabric woven from "E" glass for printed boards

Matériaux pour circuits imprimés et autres structures d’interconnexion –

Partie 6-3: Ensemble de spécifications intermédiaires pour matériaux de renfort

– Spécification des tissus finis en verre "E" pour circuits imprimés

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.180 ISBN 978-2-8322-7070-7

– 2 – IEC 61249-6-3:2023 © IEC 2023
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Visual requirements . 9
5 Physical requirements . 10
5.1 Fabric count . 10
5.2 Weave type . 10
5.3 Fabric thickness . 10
5.4 Fabric weight . 10
5.5 Fabric length . 10
5.6 Fabric width . 10
5.7 Feather length . 10
5.8 Filament diameter . 10
5.9 Bare glass nominal measurement . 11
6 Chemical requirements . 11
7 Electrical requirements . 11
7.1 Dielectric constant . 11
7.2 Dissipation factor . 11
8 Workmanship requirements . 12
8.1 Splices . 12
8.2 Laser machinability performance . 12
8.3 Alternate fabric styles and weaves . 12
9 Quality assurance . 12
9.1 Statistical process control (SPC) . 12
9.2 Responsibility for inspection . 13
9.3 Test equipment and inspection facilities . 13
9.4 Preparation of samples . 13
9.5 Standard laboratory conditions . 13
9.6 Inspection requirements and acceptability . 13
9.6.1 General . 13
9.6.2 Sample size . 13
9.6.3 Sampling plans . 14
9.6.4 Acceptable quality level (AQL) . 14
9.7 Test methods . 14
9.7.1 Fabric appearance . 14
9.7.2 Fabric count . 15
9.7.3 Weave type . 15
9.7.4 Fabric thickness . 15
9.7.5 Weight per unit area . 15
9.7.6 Fabric length . 16
9.7.7 Fabric width . 16
9.7.8 Finish level (organic content) . 16
9.7.9 Bias or bowed filling . 17
10 Preparation for delivery . 17
10.1 Preservation and packaging . 17

10.2 Packing . 17
10.3 Marking . 17
11 Additional Information . 17
11.1 Ordering data . 17
11.2 New styles . 17
Annex A (normative) Finished fabric glass styles in SI units . 18
Bibliography . 21

Table 1 – Classification of defects . 9
Table 2 – Filament Thdiameter designations . 10
Table 3 – Bare glass nominal measurements . 11
Table 4 – Sample size per number of rolls shipped . 13
Table 5 – Sample size per length of individual roll shipped and

the acceptable quality level . 14

– 4 – IEC 61249-6-3:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MATERIALS FOR PRINTED BOARDS AND OTHER
INTERCONNECTING STRUCTURES –
Part 6-3: Sectional specification set for reinforcement materials –
Specification for finished fabric woven from "E" glass for printed boards

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 61249-6-3 has been prepared by IEC technical committee 91: Electronics assembly
technology. It is an International Standard.
This first edition cancels and replaces the IEC/PAS 61249-6-3 published in 2011. This edition
constitutes a technical revision.
The text of this International Standard is based on the following documents:
Draft Report on voting
91/1680/CDV 91/1828A/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 61249-6-3:2023 © IEC 2023
MATERIALS FOR PRINTED BOARDS AND OTHER
INTERCONNECTING STRUCTURES –
Part 6-3: Sectional specification set for reinforcement materials –
Specification for finished fabric woven from "E" glass for printed boards

1 Scope
This part of IEC 61249 covers finished fabrics woven from ‘‘E’’ glass electrical grade glass fibre
yarns that are intended as a reinforcing material in laminated plastics for electrical and
electronic use. All fabrics covered by this specification are plain weave.
This specification determines the nomenclature, definitions, general and chemical requirements
for the glass, and physical requirements for finished woven glass fibre fabrics.
Annex A of this document provides a style designator for each finished fabric glass style, with
specifications on yarn, fabric count, thickness and weight in both SI and US system.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
AQL
Acceptable Quality Level
maximum number of defects per hundred units that can be considered satisfactory as a process
average
3.2
bias
filling yarns are off-square to the warp ends
3.3
bow
filling yarns lie in an arc across the width of the fabric

3.4
creases
ridge in the fabric caused by a fold or wrinkle being placed under pressure
3.5
defect
substandard area in a fabric
3.5.1
major defect
defect that is likely to result in failure, or to reduce materially the usability of the unit of product
for its intended purpose
3.5.2
minor defect
defect that is not likely to reduce materially the usability of the unit of product for its intended
purpose
3.6
E-glass
Electrical Glass which is to be used for printed board applications, is a continuous filament
glass yarn with a chemical composition by weight that is within the following limits:

B2O3 5 % to 10 %
CaO 16 % to 25 %
Al2O3 12 % to 16 %
SiO2 52 % to 56 %
MgO 0 % to 5 %
Na2O / K2O 0 % to 2 %
TiO2 0 % to 0,8 %
Fe2O3 0,05 % to 0,4 %
F2 0 % to 10 %
Note 1 to entry: For convenience, the composition of borosilicate glass is often expressed in terms of oxides (B2O3,
SiO2, Al2O3, Na2O, CaO, etc.). This does not imply anything about the nature and structure of glass. Borates are
network formers and are part of the structure of borosilicate glass. All raw materials are completely consumed during
manufacturing, and no raw materials are present in the final product.
3.7
permittivity for bulk form E glass
reference dielectric constant to be used for printed board applications
3.8
feather length
distance from last warp end to the end of the pick
3.9
fabric finish
treatment of fabric to aid in compatibility with resins
3.10
fish eye
small area of fabric which resists resin wetting and can be caused by the resin system, fabric
or treatment
– 8 – IEC 61249-6-3:2023 © IEC 2023
3.11
hollow filament
individual filament within a glass yarn bundle that contains a longitudinal void
3.12
Leno end out
missing wrapper warp end from the edge of the fabric
3.13
lot
collection of units produced in one continuous, uninterrupted finish run from which a sample is
drawn and inspected or tested to determine conformance with the acceptability criteria.
3.14
mark
heavy or light area in fabric due to excessive or less filling yarns
3.14.1
heavy mark
filling defect extending across the width of the fabric containing two picks/inch in excess of the
nominal count
3.14.2
light mark
filling defect extending across the width of the fabric containing two picks/inch less than the
nominal count
3.15
pick
filling yarn running crosswise the entire width of a fabric
3.16
broken pick
filling yarn missing from a portion of the width of the fabric
3.17
mis-picks
break in the pattern of cloth from selvage to selvage caused by a missing filling yarn
3.18
plain weave
fabric configuration where each warp end should go over one pick and under the next, and each
pick should go over one warp end and under the next
3.19
split
opening in the fabric resulting from either the pick or end breaking in two
3.20
spread glass fabric
woven glass fabric, the warp and/or fill yarns of which, through mechanical action, are flattened
(spread out) such that the radial cross sectional aspect ratio (ratio of length of major and minor
axes) is increased and the percentage of open space between yarns per unit area is decreased,
as compared to a non-spread fabric of the same style

3.21
TEX system
system for expressing linear density of yarn or other textile strand expressed as
grams/kilometer
3.22
waste
lump or collection of yarn or filament woven into the fabric where accumulated contamination
off the loom has found its way into the fabric
3.23
waviness
cloth is woven under varying tensions preventing even placement of picks resulting in
alternating thick and thin places
4 Visual requirements
When specified by purchase contract, the fabric is examined in accordance with 9.7.1. Visual
defects shall be identified and classified per Table 1 and meet the AQL defined in 9.6.3 and
9.6.4 as specified.
Table 1 – Classification of defects
Visual Defect Description Classification
Pick line distortion from horizontal by more than 2,5 %
a
Bias or bowed filling Major
for entire width
Baggy or wavy cloth Clearly noticeable per 9.7.1 Major
Cut or tear > 6,5 mm in any direction (body only) Major
Spots, streaks, stains, foreign
Clearly noticeable Major
inclusions
Broken or missing ends or
2 or more continuous, regardless of length Major
picks
Light marks > 6,5 mm in width Major
2 picks/2,54 cm less than nominal Minor
Heavy marks Puckering clearly noticeable Major
2 picks/2,54 cm more than nominal Minor
Crease Hard embedded and folded over on self Major
Waste Clearly noticeable > 6,5 mm Major
Clearly noticeable ≤ 6,5 mm Minor
Weave separation Clearly noticeable >3,175 mm Major
Leno ends out >5 m Major
≤5 m Minor
Feather length >5 mm running >4,5 m Major
>5 mm running ≤4,5 m Minor
a
It is important that as a target for the future, the non-homogeneous bow (i.e., a bow not stretching across the
width of material) should be reduced.

– 10 – IEC 61249-6-3:2023 © IEC 2023
5 Physical requirements
5.1 Fabric count
Fabric count shall be evaluated in accordance with 9.7.2. The nominal fabric count for each
style shall be as specified in Annex A. For fabrics not listed, the nominal fabric count shall be
as agreed upon between user and supplier. The actual average count of warp ends or filling
picks shall be within ± 2/2,54 cm of the nominal count.
5.2 Weave type
Weave type shall be determined in accordance with 9.7.3. This specification only addresses
plain weave.
5.3 Fabric thickness
Fabric thickness shall be determined in accordance with 9.7.4. The nominal fabric thickness for
each style shall be as specified in Annex A.
5.4 Fabric weight
Fabric weight shall be determined in accordance with 9.7.5. The nominal fabric weight for each
style shall be as specified in Annex A and shall meet the tolerance listed.
5.5 Fabric length
Fabric length shall be determined in accordance with 9.7.6 and shall be as specified on the
purchase order. The length of the fabric shall be within ± 1 % of the value specified.
5.6 Fabric width
Fabric width shall be determined in accordance with 9.7.7 and shall be as specified on the
purchase order. The width of the fabric shall be within (-0/+13) mm of the value specified. If the
fabric has coated and cut (C&C) edges, the width shall be within (-0/+5) mm of the value
specified.
5.7 Feather length
The feather length shall not exceed 5,0 mm.
5.8 Filament diameter
The nominal filament diameter and the range of averages for products used in electrical
laminates are as given in Table 2. The filament diameters are to be certified by the yarn supplier
when requested.
Table 2 – Filament diameter designations
Designation Nominal diameter Range of averages
(SI) (μm) (μm)
4 4 3,50 to 4,70
4,5 4,5 3,56 to 5,08
5 5 4,80 to 5,87
6 6 5,84 to 7,16
7 7 6,40 to 7,82
9 9 8,46 to 10,34
5.9 Bare glass nominal measurement
Bare glass nominal measurement (meters) shall be as defined in Table 3.
Table 3 – Bare glass nominal measurements
Yarn Nominal length per unit weight
SI Nomenclature SI (m/kg)
4 1,65 1x0 604,773
4 2,20 1x0 453,571
4 3,31 1x0 302,385
4,5 2,76 1x0 362,864
4,5 4,13 1x0 241,905
a
5 2,75 1x0 362,864
5 5,5 1x0 181,432
6 8,27 1x0 120,955
5 11 1x0 90,716
6 16,5 1x0 60,477
5 22 1x0 45,358
7 22 1x0 45,358
9 33 1x0 30,239
6 33 1x0 30,239
7 41 1x0 25,199
7 45 1x0 22,175
6 49 1x0 20,159
9 68 1x0 14,716
9 74 1x0 13,507
9 99 1x0 10,080
9 134 1x0 7,459
a
1/0 or 1x0 = Single yarn which has not been combined.

6 Chemical requirements
The finish level of the fabric shall be determined in accordance with 9.7.8. The organic content
of the finish fabric shall be no less than 0,05 % and no more than 0,30 %, unless otherwise
agreed upon between user and supplier.
7 Electrical requirements
7.1 Dielectric constant
The dielectric constant of bulk form E-glass when measured at 1 GHz shall be 7,1 +/-0,3 units
when tested using parallel plate analysis or equivalent.
7.2 Dissipation factor
The dissipation factor when measured at 1 GHz shall be as agreed upon between user and
supplier.
– 12 – IEC 61249-6-3:2023 © IEC 2023
8 Workmanship requirements
8.1 Splices
Unless otherwise specified, the maximum allowable number of splices is one per 915 m, with a
minimum length between splices of 137 m. All splices shall be flagged and compatible with resin
solvents. Splices shall not lose strength and shall withstand treater stresses.
8.2 Laser machinability performance
Laser machinability performance is recognized as a significant fabric style attribute.
Requirements for laser machinability will be considered as a specification sheet element at such
time that a standardized test method and performance level requirements are developed. Until
then, the test method and performance level requirements shall be as agreed upon between
user and supplier.
8.3 Alternate fabric styles and weaves
For alternate fabric styles and weaves not covered by this specification, requirements shall be
as agreed upon the user and supplier.
9 Quality assurance
9.1 Statistical process control (SPC)
SPC utilizes systematic statistical techniques to analyze a process or its outputs. The purpose
of these analyses is to take appropriate actions to achieve and maintain a state of statistical
control, and to assess and improve process capability. The primary goal of SPC is to continually
reduce variation in processes, products or services in order to provide product meeting or
exceeding real or important customer requirements.
Depending on the progress made in implementing SPC on a particular product, an individual
supplier may demonstrate compliance to specification with any of the following:
• quality conformance evaluations;
• end-product control;
• in-process product control;
• process parameter control.
An individual supplier may choose to use a combination of the four assurance techniques listed
to prove compliance. For example, a product with 15 characteristics may meet specifications
by quality conformance evaluations on two characteristics, in-process evaluations on five
characteristics and process parameter control for five characteristics. The remaining three
characteristics meet specifications by a combination of in-process control and quality
conformance evaluations. Evidence of compliance to the specification at the level of SPC
implementation claimed is auditable by the customer or appointed third party.
Requirements are dynamic in nature and are based on what is accepted in the worldwide market.
Requirements may be stated as a reduction of variation around a target value, as opposed to
just meeting the specification, drawing, etc.

9.2 Responsibility for inspection
If specified on the purchase order, all fabrics shall be inspected as per 9.6, according to the
test methods specified herein. Except as otherwise specified in the purchase order, the supplier
may use his own or any other facility suitable for the execution of the inspection requirements
herein, unless disapproved by the procuring authority. The procuring authority reserves the
right to perform any of the inspections set forth in the specification where such inspections are
deemed necessary to assure supplies and service are performed to the prescribed requirements.
9.3 Test equipment and inspection facilities
Test and measuring equipment and inspection facilities of sufficient accuracy, quality, and
quantity to permit performance of the required inspection shall be established and maintained
by the supplier.
9.4 Preparation of samples
Unless otherwise specified herein or in the test methods, samples shall be prepared in
accordance with standard in-house procedures. If a referee method is required, it shall be as
agreed upon between user and supplier.
9.5 Standard laboratory conditions
Unless otherwise specified herein, all sample conditioning and testing shall be performed in
accordance with the test conditions specified in the general requirements.
9.6 Inspection requirements and acceptability
9.6.1 General
The acceptability of the product shall be in accordance to 9.6.3 or 9.6.4 as specified in the
purchase order.
Registration of a supplier’s quality system to ISO 9001 or other equivalent standard may be
acceptable in lieu of the final inspection of product as agreed between user and supplier.
9.6.2 Sample size
The definition of a sample size for use shall be in proportion to the size of the lot, i.e., the
number of rolls and/or total meters to be shipped, per Table 4 and Table 5.
Table 4 – Sample size per number of rolls shipped
Number of rolls to be
Number of rolls shipped inspected Code letter
2-8 2 A
9-15 3 B
16-25 5 C
26-50 8 D
51-90 13 E
91-150 20 F
– 14 – IEC 61249-6-3:2023 © IEC 2023
Table 5 – Sample size per length of individual roll shipped and
the acceptable quality level
Roll size Sample size Code letter 2,5 % AQL
(m) (m) Accept Reject
138 - 256 30 G 2 3
257 - 457 45 H 3 4
458 – 1 097 73 J 5 6
1 098 – 2 926 115 K 7 8
2 927 – 9 145 180 L 10 11
9.6.3 Sampling plans
Sampling plans sufficient to ensure an AQL of 2,5 % shall be used (see Table 4 and Table 5)
and shall be substantiated by the supplier and available for inspection by the user on request.
For small lots, one or more defects shall be cause for rejection. Resubmitted lots shall be
inspected using tightened inspection. Such lots shall be separated from new lots and shall be
clearly identified as re-inspected lots.
9.6.4 Acceptable quality level (AQL)
No 1 meter shall be penalized with more than one major defect.
A continuous defect shall be counted as one defect for each warp-wise meter or fraction thereof
in which it occurs.
The occurrence of an average of eight major defects in 100 m, or the single major defect of
"baggy or wavy cloth," shall constitute cause for rejection of the roll in which the defects occur.
Four minor defects shall be considered as the equivalent of one major defect.
Latent defects or defects that appear during or after treatment can occur to make the product
unacceptable for its intended use. The acceptable level of these defects and the resolution of
any rejects arising must be negotiated between user and supplier. Latent defects that are
difficult to identify on the fabric before treatment are:
• broken glass filaments that result in protrusion of glass filaments and resin;
• discolorations caused by binder streaks or incomplete heat cleaning;
• fish eye (see 3.10);
• hollow filament (see 3.11).
9.7 Test methods
9.7.1 Fabric appearance
Fabric shall be inspected while traversing over a flat viewing area of at least one linear meter
by the full width of the fabric.
The light source should be mounted on a different plane parallel to the viewing surface of the
fabric so as to illuminate the surface with overhead perpendicular light.
View and inspect the fabric from a distance of approximately 1 m.

Count all defects except where two or more defects represent a single local condition (all within
one linear meter). In this case, count only the more serious defect as one defect. A continuous
defect is counted as one defect for each linear meter or fraction thereof in which it appears.
Classify the defects as listed in Table 1.
9.7.2 Fabric count
Lay fabric sample on a flat surface free of tension, creases, or wrinkles. Using any suitable
magnifying or counting device (such as pick glass or ruler) count the number of yarns in a cm
or in area for both warp and fill directions. Five successive counts should be made, evenly
spaced on a diagonal across the width of the sample. Counts should not be made within 1/10th
of the width of the sample from the edge.
Average the five counts and round off to the nearest 0,1 yarn count per cm. Report results,
stating the warp count first.
EXAMPLE Fabric count for 7628 Style Fabric = 17,3 x 12,2 per cm.
9.7.3 Weave type
Place the fabric sample on a flat surface with the warp direction extending away from the
observer. Examine the sample with either the naked eye or low power magnification (if needed).
Select a starting point on the surface of the fabric where a warp end is raised over a filling pick
- raiser yarn. (A filling pick raised over a warp end is a sinker yarn.)
Plot the weave construction on graph paper. Plot from left to right from the first raiser yarn,
showing raiser yarns as marked blocks and sinker yarns as unmarked blocks until a minimum
two repeats of the pattern are observed. In a like manner, plot up from the first raiser yarn until
a minimum of two repeats of the pattern are observed corresponding to each designated block
in the left-right pattern.
A plain weave fabric plot will exhibit a uniform checker board pattern.
9.7.4 Fabric thickness
Fabric thickness is measured with apparatus equipped with a 6,35 mm diameter presser foot
and anvil and 1,76 kg/cm load.
Make ten thickness measurements across the width of the sample; record to the nearest
0,0025 mm. Do not measure within 1/10th the sample width from the edge.
Average the ten readings and report the fabric thickness to the nearest 0,002 5 mm.
9.7.5 Weight per unit area
Prepare a fabric specimen or a number of smaller die cut specimens having a total minimum
area of 290 cm . Do not take specimens closer than 1/10 of the fabric width to a selvage or cut
edge. Measure specimen dimensions to the nearest 0,5 mm.
Weigh specimen (or small specimens together) to within ± 0,01 % of the weight on a balance.
During cutting and weighing, any loose yarns unraveling from the cut shall also be weighed with
the specimen. Report average of the side, centre, side specimens, or indicate if only a single
determination per fabric specimen were made.

– 16 – IEC 61249-6-3:2023 © IEC 2023
[Calculate the weight in grams per square meter.]
[Grams per Square Meter (GSM) = G / A]
where:
G = Total weight of specimen(s) in grams.
A = Total area of specimen(s) in length by width measured in square meters.
9.7.6 Fabric length
The fabric roll length shall be measured by the clock method. The measuring device consists
of a wheel or pair of wheels mounted on a free running axle connected to a counting mechanism
graduated to read in meters and centimeters]. The surfaces of the wheels are to be covered
with a friction material to prevent slippage. The circumference of the wheel is to be known and
synchronized with the mechanism to read in meters.
The measuring device is to be mounted in such a way that movement of the fabric through the
machine will turn the wheels.
The roll will be measured from beginning to end and the length reported to the nearest meter.
9.7.7 Fabric width
Place the fabric on a smooth horizontal surface without tension in any direction. Measure the
width to the nearest 2,5 mm perpendicular to the edges using a measuring stick or steel tape.
In the case of ‘‘feathered’’ or ‘‘fringed’’ edge material, the measurement will be from the
outermost warp yarns on each side of the fabric.
9.7.8 Finish level (organic content)
Cut a fabric specimen from the center of the fabric with a weight of 6 g or total minimum area
of 290 cm . Fold the sample in from all edges and tuck it into a compact square or triangle with
no loose strings exposed.
1) Condition in oven at 121 °C ± 5 °C for a minimum of one hour. Conditioning is often omitted
in current lab practices, but shall be used to resolve finish level conflicts between user and
supplier.
2) Cool in desiccator or equivalent for a minimum of 10 minutes.
3) Weigh the sample to the nearest 0,1 mg and record as W .
4) Place the sample in a muffle furnace at 625 °C ± 30 °C for 20 ± 2 min.
5) Cool in desiccator or equivalent for a minimum of 10 min.
6) Reweigh the sample to the nearest 0,1 mg, record as W , and calculate the organic content
as follows:
% Organic content = [(W -W ) / W ] x 100
1 2 1
W = Initial weight
W = Burned off weight
9.7.9 Bias or bowed filling
Place the glass fabric against a right angle ruler or over a right angle edge of a flat table.
(Handle the glass gently and evenly so not to distort it during testing.) The warp (machine)
direction or the length of the cloth should be running in the line of sight, the fill (width of fabric)
should be perpendicular. Pick-up the fill yarn at one corner of the table or right angle fixture
and follow it as it runs across the full width of the web. It should approximately be parallel to
the base line. If it is running under an angle, mark with a felt marker on the end of the yarn on
the opposite side of the corner from which you started. Measure the maximum distance between
the mark and the baseline.
[Distance / Fabric Width] x 100 = % distortion from horizontal
Other methods for measuring distortion may be used as agreed between user and supplier.
10 Preparation for delivery
10.1 Preservation and packaging
Preservation and packaging shall be in such a manner as to ensure delivery in a condition that
will pass the requirements of this specification.
10.2 Packing
Packing shall be as specified (see Clause 6).
10.3 Marking
In addition to any special marking required by the contract or order, each unit package, exterior
container and unitized load shall be clearly marked to assure product identity.
11 Additional information
11.1 Ordering data
The subcontract or purchase order should specify the following:
1) title number and date of this specification;
2) style designation (see Annex A);
3) fabric dimensions;
4) levels of preservations, packaging and packing;
5) marking;
6) any deviations from this specification.
11.2 New styles
A new or altered woven fibre glass style shall be considered for addition to IEC 61249-6-3 when
the appropriate style and yarn designations and format as listed in Annex A are submitted to
IEC TC 91 WG4. When a new style is submitted, conversion to SI units will be done.

– 18 – IEC 61249-6-3:2023 © IEC 2023
Annex A
(normative)
Finished fabric glass styles in SI units
a
Style Fabric count Yarn (SI) Thickness Nominal Weight
Availability
warp x fill weight tolerance
2 2
(Per cm) (mm)
(g/m ) (g/m )
(reference only)
101 29,5 x 29,5 5 2,75 1x0 5 2,75 1x0 0,024 16,3 15,2 – 17,3 1
104 23,6 x 20,5 5 5,5 1x0 5 2,75 1x0 0,028 18,6 18,0 – 19,3 1
106 22,0 x 22,0 5 5,5 1x0 5 5,5 1x0 0,033 24,4 23,4 – 25,4 1
1078 21,3 x 21,3 5 11 1x0 5 11 1x0 0,043 47,8 46,8 – 49,2 1
1080 23,6 x 18,5 5 11 1x0 5 11 1x0 0,053 46,8 45,1 – 48,5 1
1081 27,6 x 23,6 5 11 1x0 5 11 1x0 0,060 58,3 56,4 – 60,6 1
1280 23,6 x 23,6 5 11 1x0 5 11 1x0 0,056 52,9 51,5 – 54,2 1
b b
1500 19,3 x 16,5 0,149 164,1 157,7 – 170,5 1
7 45 1x0 7 45 1x0
b b
1501 18,1 x 17,7 0,140 165,0 158,0 – 171,0 1
7 45 1x0 7 45 1x0
1504 23,6 x 19,7 6 33 1x0 6 33 1x0 0,125 148,0 142,8 – 153,2 1
1651 20,0 x 10,8 9 33 1x0 9 74 1x0 0,135 146,2 142,1 – 150,3 1
b b
1652 20,5 x 20
...