SIST EN ISO 844:2026

• Abstract:

  This document specifies methods for determining the compressive strength, the corresponding compressive strain, the compressive stress at 10 % nominal compressive strain, and the compressive modulus of rigid cellular plastics.; Two procedures are specified. Procedure A and Procedure B.; Procedure A utilizes the compression plate displacement for the nominal property determination. It is used to determine:; compressive strength and the corresponding nominal compressive strain;; compressive stress at 10 % nominal compressive strain;; nominal compressive modulus.; Procedure B uses an extensometer and determines the conventional properties. It is used to determine:; compressive strength and the corresponding compressive strain;; compressive modulus.

• Status: Published
• Public Enquiry End Date: 28-Apr-2025
• Publication Date: 21-Jul-2026
• ICS: 83.100 - Cellular materials
• Technical Committee: IPMA - Polimer materials and products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 21-Jul-2026
• Due Date: 25-Sep-2026
• Completion Date: 22-Jul-2026
• Ref Project: EN ISO 844:2026 - Rigid cellular plastics - Determination of compressive properties (ISO 844:2026)

• Refers: SIST ISO 1923:1996 - Cellular plastics and rubbers -- Determination of linear dimensions
• Effective Date: 22-Jul-2026
• Referred By: SIST EN 17333-4:2020 - Characterization of One Component Foam - Part 4: Mechanical strength
• Effective Date: 15-Jul-2026
• Referred By: SIST EN 17415-1:2020 - District cooling pipes - Bonded single pipe systems for directly buried cold water networks - Part 1: Factory made pipe assembly of steel or plastic service pipe, polyurethane thermal insulation and a casing of polyethylene
• Effective Date: 15-Jul-2026
• Referred By: SIST EN 253:2020 - District heating pipes - Bonded single pipe systems for directly buried hot water networks - Factory made pipe assembly of steel service pipe, polyurethane thermal insulation and a casing of polyethylene
• Effective Date: 15-Jul-2026
• Referred By: SIST EN ISO 5139:2023 - Dentistry - Polymer-based composite machinable blanks (ISO 5139:2023)
• Effective Date: 28-Jan-2026
• Revised: SIST EN ISO 844:2021 - Rigid cellular plastics - Determination of compression properties (ISO 844:2021)
• Effective Date: 18-Jan-2023

SIST EN ISO 844:2026 is the European adoption of ISO 844:2026 for rigid cellular plastics. It specifies how to determine compressive strength, compressive strain, compressive stress at 10 % nominal compressive strain, and compressive modulus. The document is written for testing laboratories, manufacturers, and specifiers that need comparable compression data for rigid cellular plastics.

What does SIST EN ISO 844:2026 specify?

SIST EN ISO 844:2026 covers methods for measuring the compressive properties of rigid cellular plastics under constant displacement loading between rigid plates. It defines two procedures: Procedure A gives nominal properties from compression plate displacement, and Procedure B gives conventional properties from an extensometer on the specimen.

The document is organized into clauses on scope, normative references, terms and definitions, symbols, principle, apparatus, test specimens, procedure, result expression, precision, and test report. Annex A is informative and shows extensometer arrangements for Procedure B.

Annex	What it covers
Annex A	Extensometer for Procedure B, including mechanical and optical arrangements

What are the key requirements of SIST EN ISO 844:2026?

Apparatus and calibration

SIST EN ISO 844:2026 requires a compression-testing machine with two rigid, ground, plane-parallel plates that can cover the force and displacement range of the test. The plates must be stiff enough not to influence the result, aligned axially within 1:1 000, and flat and perpendicular to the loading axis within the stated limits. In practice, this reduces machine-induced error, which matters because the standard compares small differences in slope and force.

For Procedure A, the machine must measure plate displacement continuously with the stated accuracy. For Procedure B, the machine must use an extensometer that measures specimen displacement directly and meets class 1 of ISO 9513. The force-measuring system must meet class 1 of ISO 7500-1, and the equipment must be calibrated periodically to ISO 7500-1 and ISO 9513.

Test specimens and conditioning

Clause 7 sets the preferred specimen geometry as a right prism of 100 mm by 100 mm with a 50 mm thickness. Square or circular specimens are also allowed within the stated area range, and the minimum thickness depends on the product and the procedure. This matters because specimen size and thickness can change the measured compression response.

The specimens must be cut with the base normal to the compression direction in use, and the cutting method must not change the cellular structure. Moulded skins are removed unless they remain integral in use. The standard also requires conditioning in one of the stated atmospheres for at least 6 hours, and the test must be carried out in the same environment. In practice, that keeps moisture and temperature effects consistent.

Procedure A and Procedure B

Clause 8 requires the specimen to be placed centrally between the plates, the extensometer to be attached for Procedure B, and the machine to run at a speed close to 10 % of the original thickness per minute. The specimen is compressed until the required force values are obtained, and a force-displacement curve is recorded. The speed target is important because compression results depend on rate.

Procedure A uses relative plate displacement to determine nominal compressive properties. Procedure B uses direct specimen displacement to determine conventional properties. The introduction explains why this difference matters: plate displacement includes machine effects, while direct specimen measurement better reflects specimen deformation.

Result calculation and curve interpretation

Clause 9 defines compressive strength as maximum force divided by initial cross-sectional area, with the result taken at the relevant point on the curve. For Procedure A, the standard also determines nominal compressive strain and compressive stress at 10 % nominal compressive strain. For Procedure B, it determines compressive strain and compressive modulus.

The standard gives rules for different force-displacement curve shapes, including cases with force-drop and cases without it. If a toe region appears at the start of the curve, it must be compensated before strain is calculated. For modulus, the standard uses the steepest linear range below the proportional limit, found by dividing the relevant part of the curve into at least six segments and comparing adjacent slopes. This makes the reported modulus more consistent across foams with non-linear early behavior.

Precision and reporting

Clause 10 gives precision information from interlaboratory tests for both procedures. For Procedure A, the precision data cover compressive strength, stress at 10 % nominal compressive strain, and nominal compressive modulus. For Procedure B, the precision data cover compressive strength and compressive modulus. This helps users judge how much spread to expect between laboratories.

Clause 11 lists what the test report must include: the reference to SIST EN ISO 844:2026, identification of the product, specimen dimensions, force direction relative to anisotropy or geometry, the procedure used, number of specimens, average results, individual values when variation is high, testing date, and any deviations. For buyers and quality teams, that report structure is what makes the result traceable and comparable.

What terms does SIST EN ISO 844:2026 define?

• Nominal compressive strain - the decrease in thickness per unit original thickness of the specimen; Procedure A uses this measure.
• Compressive strain - the decrease in length per unit original gage length of the specimen; Procedure B uses this measure.
• Compressive strength - the maximum compressive force divided by the initial cross-sectional area of the specimen.
• Compressive stress at 10 % nominal compressive strain - the force at 10 % nominal compressive strain divided by the initial area.
• Nominal compressive modulus - the slope-like value based on compressive stress and nominal compressive strain below the nominal proportional limit.
• Compressive modulus - the equivalent modulus based on compressive stress and compressive strain below the proportional limit.
• Nominal proportional limit - the upper displacement limit of the linear part of the force-nominal displacement curve.
• Proportional limit - the upper displacement limit of the linear part of the force-displacement curve.

Who uses SIST EN ISO 844:2026?

SIST EN ISO 844:2026 is used by testing laboratories, material producers, and quality control teams that need repeatable compression data for rigid cellular plastics. It is also relevant to buyers, specifiers, and technical assessors who compare supplier data or confirm that a product has been tested in a defined way. Procedure A is useful when the user needs nominal properties based on plate displacement, while Procedure B is used when direct specimen deformation is needed.

What changed in SIST EN ISO 844:2026 from the previous edition?

SIST EN ISO 844:2026 supersedes EN ISO 844:2021. The ISO foreword says this eighth edition replaces ISO 844:2021 and was technically revised.

The stated changes are:

• the term “compression” was changed to “compressive” throughout the document, including the title;
• the scope was expanded to describe Procedure A and Procedure B in more detail;
• “relative deformation” was changed to “compressive strain”;
• “nominal relative deformation” was changed to “nominal compressive strain”;
• “necking” was replaced with the more descriptive “force-drop”.

Which standards are used with SIST EN ISO 844:2026?

• ISO 291 - gives the standard atmospheres used for conditioning and testing.
• ISO 1923 - provides the method for measuring linear dimensions of the test specimens.
• ISO 7500-1 - covers calibration and verification of the force-measuring system of the testing machine.
• ISO 9513 - covers calibration of extensometer systems used in uniaxial testing.
• ISO 5725-2 - is used in clause 10 to analyse repeatability and reproducibility data from the interlaboratory tests.

What does the SIST EN ISO 844:2026 document contain?

SIST EN ISO 844:2026 contains the full test method for compression testing of rigid cellular plastics, including symbols, principle, apparatus requirements, specimen preparation, conditioning, test procedure, calculation rules, precision data, and reporting requirements. It includes figures showing example force-displacement curves for both procedures, a table linking specimen thickness to extensometer gage length, and tables with interlaboratory precision results. Annex A gives practical extensometer arrangements for Procedure B, including mechanical and optical approaches.

SLOVENSKI STANDARD
01-september-2026
Trdi penjeni polimerni materiali (trde pene) - Ugotavljanje lastnosti stiskanja (ISO
844:2026)
Rigid cellular plastics - Determination of compressive properties (ISO 844:2026)
Harte Schaumstoffe - Bestimmung der Druckeigenschaften (ISO 844:2026)
Plastiques alvéolaires rigides - Détermination des caractéristiques de compression (ISO
844:2026)
Ta slovenski standard je istoveten z: EN ISO 844:2026
ICS:
83.100 Penjeni polimeri Cellular materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 844
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2026
EUROPÄISCHE NORM
ICS 83.100 Supersedes EN ISO 844:2021
English Version
Rigid cellular plastics - Determination of compressive
properties (ISO 844:2026)
Plastiques alvéolaires rigides - Détermination des Harte Schaumstoffe - Bestimmung der
caractéristiques de compression (ISO 844:2026) Druckeigenschaften (ISO 844:2026)
This European Standard was approved by CEN on 23 June 2026.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 844:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 844:2026) has been prepared by Technical Committee ISO/TC 61 "Plastics" in
collaboration with Technical Committee CEN/TC 249 “Plastics” the secretariat of which is held by SIS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2027, and conflicting national standards shall
be withdrawn at the latest by January 2027.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 844:2021.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 844:2026 has been approved by CEN as EN ISO 844:2026 without any modification.

International
Standard
ISO 844
Eighth edition
Rigid cellular plastics —
2026-06
Determination of compressive
properties
Plastiques alvéolaires rigides — Détermination des
caractéristiques de compression
Reference number
ISO 844:2026(en) © ISO 2026
ISO 844:2026(en)
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 844:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Principle . 3
6 Apparatus . 4
6.1 Testing machine .4
6.2 Devices for measuring displacement and force .4
6.2.1 Displacement .4
6.2.2 Force .4
6.2.3 Calibration . . .5
6.3 Devices for measuring the dimensions of the test specimens .5
7 Test specimens . 5
7.1 Dimensions .5
7.2 Preparation .5
7.3 Number .5
7.4 Conditioning.5
8 Procedure . 6
9 Expression of results . 6
9.1 General .6
9.2 Compressive strength and compressive strains .8
9.2.1 Compressive strength .8
9.2.2 Nominal compressive strain (procedure A) .8
9.2.3 Compressive strain (procedure B) .8
9.3 Compressive stress at 10 % nominal compressive strain (procedure A) .8
9.4 Modulus.8
9.4.1 General .8
9.4.2 Nominal compressive modulus (procedure A) .9
9.4.3 Compressive modulus (procedure B) .9
10 Precision . 9
10.1 Procedure A .9
10.2 Procedure B .10
11 Test report . 10
Annex A (informative) Extensometer for Procedure B .12
Bibliography .13

iii
ISO 844:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 10, Cellular
plastics, in collaboration with the European Committee for Standardization (CEN) Technical Committee
CEN/TC 249, Plastics, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This eighth edition cancels and replaces the seventh edition (ISO 844:2021), which has been technically
revised.
The main changes are as follows:
— the term “compression” changed to “compressive” throughout the document, including the title;
— the scope has been modified to include details of Procedure A and Procedure B;
— “relative deformation” has been changed to “compressive strain”;
— “nominal relative deformation” has been changed to “nominal compressive strain”;
— “necking” has been changed to the more descriptive “force-drop”.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO 844:2026(en)
Introduction
For the determination of compressive properties, it is common practice to apply a uniform compressive
deformation to a standard test specimen, especially for quality assurance. However, the test specimen has
a complex and inhomogeneous deformation state, under compression, which is not subjected to further
analysis in such an evaluation. Measurement results are, therefore, not easily transferable to other test
specimens or products. This document describes Procedure A, which determines the nominal compressive
properties. Procedure B determines conventional compressive properties.
Procedure A employs relative plate displacement for the determination of compressive properties.
Procedure B employs displacement measuring devices directly positioned on the specimen (contact or
optical extensometer) or similar devices that measure the specimen displacement.

v
International Standard ISO 844:2026(en)
Rigid cellular plastics — Determination of compressive
properties
1 Scope
This document specifies methods for determining the compressive strength, the corresponding compressive
strain, the compressive stress at 10 % nominal compressive strain, and the compressive modulus of rigid
cellular plastics.
Two procedures are specified. Procedure A and Procedure B.
Procedure A utilizes the compression plate displacement for the nominal property determination. It is used
to determine:
— compressive strength and the corresponding nominal compressive strain;
— compressive stress at 10 % nominal compressive strain;
— nominal compressive modulus.
Procedure B uses an extensometer and determines the conventional properties. It is used to determine:
— compressive strength and the corresponding compressive strain;
— compressive modulus.
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 ame
...