ASTM D737-96
(Test Method)Test Method for Air Permeability of Textile Fabrics
Test Method for Air Permeability of Textile Fabrics
SCOPE
1.1 This test method covers the measurement of the air permeability of textile fabrics.
1.2 This test method applies to most fabrics including woven fabrics, nonwoven fabrics, air bag fabrics, blankets, napped fabrics, knitted fabrics, layered fabrics, and pile fabrics. The fabrics may be untreated, heavily sized, coated, resin-treated, or otherwise treated.
1.3 The values stated in SI units are to be regarded as the standard. The values stated in inch-pound units may be approximate.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D737–96
Standard Test Method for
Air Permeability of Textile Fabrics
This standard is issued under the fixed designation D 737; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This test method covers the measurement of the air 3.1 Definitions—For definitions of other textile terms used
permeability of textile fabrics. in this test method refer to Terminology D 123.
1.2 This test method applies to most fabrics including 3.2 Definitions of Terms Specific to This Standard:
woven fabrics, nonwoven fabrics, air bag fabrics, blankets, 3.2.1 air permeability, n—the rate of air flow passing
nappedfabrics,knittedfabrics,layeredfabrics,andpilefabrics. perpendicularly through a known area under a prescribed air
The fabrics may be untreated, heavily sized, coated, resin- pressure differential between the two surfaces of a material.
treated, or otherwise treated. 3.2.1.1 Discussion—Air permeability of fabric at a stated
1.3 The values stated in SI units are to be regarded as the pressure differential between two surfaces of the fabric is
3 2
standard. The values stated in inch-pound units may be generally expressed in SI units as cm /s/cm and in inch-pound
3 2
approximate. units as or ft /min/ft calculated at operating conditions.
1.4 This standard does not purport to address all of the 3.2.2 cross-machine direction, CD, n—the direction in the
safety concerns, if any, associated with its use. It is the plane of the fabric perpendicular to the direction of manufac-
responsibility of the user of this standard to establish appro- ture.
priate safety and health practices and determine the applica- 3.2.2.1 Discussion—This term is used to refer to the direc-
bility of regulatory limitations prior to use. tion analogous to coursewise or filling direction in knitted or
woven fabrics, respectively.
2. Referenced Documents
3.2.3 fabric, in textiles, n—a planar structure consisting of
2.1 ASTM Standards:
yarns or fibers.
D 123 Terminology Relating to Textiles 3.2.4 machine direction, MD, n—the direction in the plane
D 1776 Practice for Conditioning Textiles for Testing
of the fabric parallel to the direction of manufacture.
D 2904 Practice for InterlaboratoryTesting of aTextileTest
3.2.4.1 Discussion—This term is used to refer to the direc-
Method That Produces Normally Distributed Data tion analogous to warpwise or warp direction in knitted or
D 2906 Practice for Statements on Precision and Bias for
woven fabrics, respectively.
Textiles
4. Summary of Test Method
F 778 Methods for Gas Flow Resistance Testing of Filtra-
tion Media 4.1 The rate of air flow passing perpendicularly through a
2.2 ASTM Adjuncts: known area of fabric is adjusted to obtain a prescribed air
TEX-PAC pressure differential between the two fabric surfaces. From this
rate of air flow, the air permeability of the fabric is determined.
NOTE 1—TEX-PAC is a group of programs on floppy disks available
through ASTM Headquarters, 100 Barr Harbor Drive, West Consho-
5. Significance and Use
hocken, PA 19428.
5.1 This test method is considered satisfactory for accep-
tance testing of commercial shipments since current estimates
of between-laboratory precision are acceptable, and this test
This test method is under the jurisdiction ofASTM Committee D13 onTextiles
and is the direct responsibility of Subcommittee D13.59 on Fabric Test Methods,
method is used extensively in the trade for acceptance testing.
General.
5.1.1 In case of a dispute arising from differences in
Current edition approved Feb. 10, 1996. Published April 1996. Originally
reported test results when using this test method for acceptance
published as D 737 – 43 T. Discontinued November 1995 and reinstated as
testing of commercial shipments, the purchaser and the sup-
D 737 – 96.
Annual Book of ASTM Standards, Vol 07.01.
plier should conduct comparative tests to determine if there is
Annual Book of ASTM Standards, Vol 14.02.
a statistical bias between their laboratories. Competent statis-
A PC program on floppy disk for Analyzing Committee D-13 interlaboratory
tical assistance is recommended for the investigation of bias.
data are available from ASTM Headquarters. For a 3 ⁄2-in. disk, request PCN:12-
429040-18. For a 5 ⁄4-in. disk, request PCN:12-429041-18. As a minimum, the two parties should take a group of test
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D737
specimens that are as homogeneous as possible and that are clamping ring 20 mm (0.75 in.) wide and 3 mm (0.125 in.)
from a lot of material of the type in question. Test specimens thick around the test area above and underneath the test
then should be randomly assigned in equal numbers to each specimen.
laboratory for testing. The average results from the two
NOTE 3—Since air leakage may affect test results, precautions must be
laboratories should be compared using the appropriate statis-
taken, especially with very heavy or lofty fabrics, to prevent leakage. The
tical analysis and an acceptable probability level chosen by the
use of a weighted ring and rubber gaskets on the clamp surfaces has been
two parties before testing is begun. If a bias is found, either its
found to be helpful. Test Method F 778 describes a series of usable
clamping adaptions to eliminate edge leakage. Gaskets should be used
cause must be found and corrected, or the purchaser and the
with caution because in some cases, and with repeated-use gaskets may
supplier must agree to interpret future test results with consid-
deform resulting in a small change in test area. A weighted ring can be
eration of the known bias.
used with fabrics, such as knits or those that readily conform to the test
5.2 Air permeability is an important factor in the perfor-
head. The weighted ring is not recommended for lofty or stiff fabric.
mance of such textile materials as gas filters, fabrics for air
6.1.3 Means for drawing a steady flow of air perpendicu-
bags, clothing, mosquito netting, parachutes, sails, tentage, and
larly through the test area and for adjusting the airflow rate that
vacuum cleaners. In filtration, for example, efficiency is
preferably provides pressure differentials of between 100 and
directlyrelatedtoairpermeability.Airpermeabilityalsocanbe
2500 Pa (10 and 250 mm or 0.4 and 10 in. of water) between
used to provide an indication of the breathability of weather-
the two surfaces of the fabric being tested. At a minimum, the
resistant and rainproof fabrics, or of coated fabrics in general,
test apparatus must provide a pressure drop of 125 Pa (12.7
and to detect changes during the manufacturing process.
mm or 0.5 in. of water) across the specimen.
5.3 Performance specifications, both industrial and military,
6.1.4 Pressure Gage or Manometer, connected to the test
have been prepared on the basis of air permeability and are
headunderneaththetestspecimentomeasurethepressuredrop
used in the purchase of fabrics where permeability is of
across the test specimen in pascals (millimetres or inches) of
interest.
water with an accuracy of 62%.
5.4 Construction factors and finishing techniques can have
6.1.5 Flowmeter, volumetric counter or measuring aperture
anappreciableeffectuponairpermeabilitybycausingachange
3 2
to measure air velocity through the test area in cm /s/cm
in the length of airflow paths through a fabric. Hot calendaring
3 2
(ft /min/ft ) with an accuracy of 62%.
can be used to flatten fabric components, thus reducing air
6.1.6 Calibration Plate, or other means, with a known air
permeability. Fabrics with different surface textures on either
permeabilityattheprescribedtestpressuredifferentialtoverify
side can have a different air permeability depending upon the
the apparatus.
direction of air flow.
6.1.7 Means of calculating and displaying the required
5.4.1 Forwovenfabric,yarntwistalsoisimportant.Astwist
results, such as scales, digital display, and computer-driven
increases, the circularity and density of the yarn increases, thus
systems.
reducing the yarn diameter and the cover factor and increasing
6.2 Cutting Dies or Templates, to cut specimens having
the air permeability.Yarn crimp and weave influence the shape
dimensions at least equal to the area of the clamping surfaces
and area of the interstices between yarns and may permit yarns
of the test apparatus (optional).
to extend easily. Such yarn extension would open up the fabric,
increase the free area, and increase the air permeability.
7. Sampling and Test Specimens
5.4.2 Increasingyarntwistalsomayallowthemorecircular,
high-density yarns to be packed closely together in a tightly 7.1 Lot Sample—As a lot sample for acceptance testing,
woven structure with reduced air permeability. For example, a randomly select the number of rolls or pieces of fabric directed
worsted gabardine fabric may have lower air permeability than in an applicable material specification or other agreement
a woolen hopsacking fabric. between the purchaser and the supplier. Consider the rolls or
pieces of fabric to be the primary sampling units. In the
6. Apparatus
absence of such an agreement, take the number of fabric rolls
or pieces specified in Table 1.
6.1 Air Permeability Testing Apparatus consisting of the
following:
NOTE 4—An adequate specification or other agreement between the
6.1.1 Test Head that provides a circular test area of 38.3
purchaser and the supplier requires taking into account the variability
cm (5.93 in. )6 0.3 %.
between rolls or pieces of fabric and between specimens from a swatch
from a roll or piece of fabric to provide a sampling plan with a meaningful
2 2
NOTE 2—Alternate test areas may be used, such as 5 cm (0.75 in. ),
producer’s risk, consumer’s risk, acceptable quality level, and limiting
2 2 2 2
6.45 cm (1.0 in. ), and 100 cm (15.5 in. ).
quality level.
6.1.2 Clamping System to Secure Test Specimens, of differ-
ent thicknesses under a force of at least 50 65N(11 6 1 lbf)
to the test head without distortion and minimal edge leakage
TABLE 1 Number of Rolls or Pieces of Fabric in the Lot Sample
underneath the test specimen.
Number of Rolls or Pieces in Number of Rolls or Pieces
6.1.2.1 Asuitable means to minimize edge leakage is to use Lot, Inclusive in Lot Sample
a 55 Type A durometer hardness polychloroprene (neoprene)
1to3 all
4to24 4
25 to 50 5
over 50 10 % to a maximum of 10 rolls or pieces
Suitable apparatus is commercially available.
D737
7.2 Laboratory Sample—For acceptance testing, take a 10.3.1 Place coated test specimens with the coated side
swatch extending the width of the fabric and approximately 1 down (towards low pressure side) to minimize edge leakage.
m (1 yd) along the lengthwise direction from each roll or piece
10.4 Make tests at the water pressure differential specified
in the lot sample. For rolls of fabric, take a sample that will in a material specification or contract order. In the absence of
exclude fabric from the outer wrap of the roll or the inner wrap
a material specification or contract order, use a water pressure
around the core of the roll of fabric. differential of 125 Pa (12.7 mm or 0.5 in. of water).
7.3 Test Specimens—From each laboratory sampling unit,
10.5 ReadandrecordtheindividualtestresultsinSIunitsas
3 2 3 2
take ten specimens unless otherwise agreed upon between cm /s/cm and in inch-pound units as ft /min/ft rounded to
purchaser and supplier. Use the cutting die or template de-
three significant digits.
scribed in 6.2, or if practical, make air permeability tests of a
10.5.1 For special applications, the total edge leakage un-
textile fabric without cutting.
derneath and through the test specimen may be measured in a
7.3.1 Cutting Test Specimens—Whencuttingspecimens,cut separate test, with the test specimen covered by an airtight
having dimensions at least equal to the area of the clamping
cover, and subtracted from the original test result to obtain the
mechanism. Label to maintain specimen identity. effective air permeability.
7.3.1.1 Take specimens or position test areas representing a
10.6 Remove the tested specimen and continue as directed
broaddistributionacrossthelengthandwidth,preferablyalong
in 10.3-10.5 until ten specimens have been tested for each
the diagonal of the laboratory sample, and no nearer the edge
laboratory sampling unit.
than one tenth its width unless otherwise agreed upon between
10.6.1 When a 95 % confidence level for results has been
the purchaser and supplier. Ensure specimens are free of folds,
agreed upon in a material specification or contract order, fewer
creases, or wrinkles. Avoid getting oil, water, grease, and so
test specimens may be sufficient. In any event, the number of
forth, on the specimens when handling.
tests should be at least four.
8. Preparation of Test Apparatus and Calibration
11. Calculation
8.1 Set-up procedures for machines from different manufac-
11.1 Air Permeability, Individual Specimens—Calculate the
turers may vary. Prepare and verify calibration of the air
air permeability of individual specimens using values read
permeability tester as directed in the manufacturer’s instruc-
3 2
directlyfromthetestinstrumentinSIunitsascm /s/cm andin
tions.
3 2
inch-pound units as ft /min/ft , rounded to three significant
8.2 When using microprocessor automatic data gathering
digits. When calculating air permeability results, follow the
systems, set the appropriate parameters as specified in the
manufacturer’s instructions as applicable.
manufacturer’s instructions.
8.3 For best results, level the test instrument. NOTE 5—For air permeability results obtained 600 m (2000 ft) above
sea level, correction factors may be required.
8.4 Verify calibration for the range and required water
pressure differential that is expected for the material to be
11.2 Air Permeability, Average—Calculate the average air
tested.
permeability for each laboratory sampling unit and for the lot.
11.3 Standard Deviation, Coeffıcient of Variation—
9. Conditioning
Calculate when requested.
9.1 Precondition the specimens by bringing them to ap-
11.4 Computer-Processed Data—When data are automati-
proximate moisture equilibrium in the standard atmosphere for
cally computer-processed, calculations are generally contained
preconditioning textiles as specified in Practice D 1776.
in the associated software. It is recommended that computer-
9.2 After preconditioning, bring the test specimens to mois-
processed data be verified again
...
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