ISO 25081:2026

• Abstract:

  This document specifies a method to test filtration performance of particulate matter of nonwovens. This document is applicable to nonwovens for air filtration.

• Status: Published
• Publication Date: 18-May-2026
• ICS: 59.080.30 - Textile fabrics
• Technical Committee: ISO/TC 38 - Textiles
• Drafting Committee: ISO/TC 38/WG 9 - Nonwovens
• Current Stage: 6060 - International Standard published
• Start Date: 19-May-2026
• Due Date: 15-Apr-2027
• Completion Date: 19-May-2026

ISO 25081:2026 is an International Standard from ISO for testing the particulate matter filtration performance of nonwovens used for air filtration. It specifies a laboratory method that covers the test setup, sample preparation, test procedure and result calculation, so users can compare filtration efficiency, airflow resistance, filter time and dust-hold capacity in a consistent way.

What does ISO 25081:2026 specify?

ISO 25081:2026 specifies a method for testing filtration performance of particulate matter in nonwovens for air filtration. The document is organized into Clauses 1 to 11, covering scope, normative references, terms and definitions, principle, apparatus, materials and reagents, sample preparation, test conditions, procedure, calculations and the test report.

The method is built around an aerosol challenge to the nonwoven, then measurement of filtration and airflow behavior as the sample loads with particles. That structure matters in practice because it tells laboratories what to prepare, what to measure, and when to stop the test.

What are the key requirements of ISO 25081:2026?

ISO 25081:2026 sets out a loading test, not just a single pass/fail measurement. The most important requirements are in Clauses 4 to 11 and define the apparatus, specimen preparation, operating conditions and reporting.

• Clause 4 - Principle: ISO 25081:2026 uses an aerosol of specified particle size as the test medium, then records initial filtration efficiency, load filtration efficiency, initial airflow resistance, final airflow resistance, filter time and dust-hold capacity. In practice, this means the test tracks how performance changes as the nonwoven loads with particles.

• Clause 5 - Apparatus: ISO 25081:2026 requires a filter tester with an aerosol generating system and a test system, plus a balance and timer. The clamp, photometers, pressure measurement and flow measurement all have defined performance needs, which matters because weak instrumentation can distort efficiency or resistance results.

• Clause 6 - Materials and reagents: ISO 25081:2026 names NaCl, DEHS, DOP or equivalent oil, and Grade 2 water for preparing the test aerosols. This gives laboratories a controlled way to produce either a solid-phase or liquid-phase aerosol challenge.

• Clause 7 - Sample preparation: ISO 25081:2026 allows unpretreated samples, temperature and humidity pretreatment, or washing pretreatment, then requires conditioning in the standard atmosphere of ISO 139 before testing. This matters because handling history can change filtration behavior, especially for products exposed to humidity, heat or laundering.

• Clause 8 - Test conditions: ISO 25081:2026 requires testing at controlled temperature and relative humidity. That keeps results comparable between laboratories.

• Clause 9 - Test procedure: ISO 25081:2026 requires the apparatus to be stabilized before testing, the airflow rate to be set, and the sample to be mounted flat with the correct face toward the airflow. The test stops when airflow resistance reaches the defined limit, so the user can compare both initial and loaded performance.

• Clause 10 - Calculation and expression of results: ISO 25081:2026 defines how to average three specimens and how to calculate dust-hold capacity from the mass gain and effective filtration area. This gives a repeatable way to report results rather than relying on a single specimen reading.

• Clause 11 - Test report: ISO 25081:2026 requires the report to identify the standard, sample, test atmosphere, aerosol concentration, chosen aerosol type, airflow rate, pretreatment, loading mass, results, test date, tester and any deviations. In practice, this is what lets another lab understand and reproduce the test.

What terms does ISO 25081:2026 define?

ISO 25081:2026 defines the vocabulary used in the test method so laboratories use the same meanings for the same measurements.

• Aerosol - a suspension of solid and/or liquid particles in a gas.
• Particulate matter (PM) - solid and/or liquid particles.
• Count median diameter (CMD) - the particle size where half the particles are larger and half are smaller.
• Filtration efficiency - the ratio describing how much particulate matter is removed by the nonwoven.
• Airflow resistance - the static pressure difference before and after the nonwoven.
• Dust-hold capacity - the amount of particulate matter held per unit area after filtration.
• Aerosol photometer - an instrument that measures light scattered by an aerosol sample.

Who uses ISO 25081:2026?

ISO 25081:2026 is used by laboratories, manufacturers and technical buyers working with nonwovens for air filtration. It is especially relevant to teams developing or qualifying filtration media for protective products, air purifiers and similar air-cleaning applications.

It also helps quality managers and test engineers who need comparable data on filtration efficiency and airflow resistance across materials, pretreatments and airflow rates. Because the method includes reporting requirements, it is also useful for supplier qualification and product comparison.

Which standards are used with ISO 25081:2026?

ISO 25081:2026 refers to several standards that support its conditioning, preparation and terminology.

• ISO 139 - gives the standard atmospheres used for conditioning and testing textiles.
• ISO 3696 - specifies the Grade 2 water used for reagents and solutions.
• ISO 6330 - provides the domestic washing and drying procedure used for washing pretreatment.
• ISO 15900 - supports the electrical mobility method recommended for particle size distribution measurement.
• ISO 16972 - supplies the source vocabulary for count median diameter.
• ISO 29464 - supplies source vocabulary for aerosol, particulate matter and aerosol photometer.

What does the ISO 25081:2026 document contain?

ISO 25081:2026 contains a schematic of the filter tester, detailed apparatus requirements, material and reagent specifications, sample pretreatment options, test conditions, a step-by-step test procedure, result calculations and the required report items. It also gives the formula used for dust-hold capacity and defines how to average results from three specimens.

For practical work, the document tells a lab how to prepare the aerosol, mount the specimen, measure filtration efficiency and pressure drop, and decide when to stop the loading test. That makes it a full test method for design evaluation, product comparison and laboratory reporting.

International
Standard
ISO 25081
First edition
Nonwovens — Test methods for
2026-05
filtration of particulate matter
Nontissés — Méthodes d'essai de filtration de matière
particulaire
Reference number
© 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
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 3
5.1 Filter tester .3
5.1.1 General .3
5.1.2 Aerosol generating system .3
5.1.3 Test system .3
5.2 Balance .4
5.3 Timer .4
6 Materials and reagents . 5
7 sample preparation . 6
7.1 General .6
7.2 Temperature and humidity pretreatment .6
7.3 Washing pretreatment .6
7.4 Sampling requirements .6
7.4.1 Sampling .6
7.4.2 Number of test specimens . . .6
8 Test conditions . 7
9 Test procedure . 7
9.1 Apparatus preparation .7
9.2 Set the airflow rate .7
9.3 Start the test .7
10 Calculation and expression of results . 8
10.1 Filtration efficiency .8
10.2 Initial airflow resistance .8
10.3 Filter time .8
10.4 Final airflow resistance .8
10.5 Dust-hold capacity .8
11 Test report . 8
Bibliography .10

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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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
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This document was prepared by Technical Committee ISO/TC 38 Textiles.
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iv
Introduction
Nonwovens are important raw materials for protective products, such as masks and air purifiers. The
performance of nonwovens has a significant impact on the quality of protective products. Among them, the
particulate matter filtration performance is the core indicator for evaluating the performance of nonwovens.
However, there is currently no independent filtration performance test method standard to uniformly
regulate the definition of terms, instrument equipment, test parameters, test procedures and result
calculation. Different countries and regions adopt different detection methods, which is not conducive
to technical comparison and exchange, and also has a certain impact on the detection and technological
development of nonwovens filtration performance. It is necessary to establish a separate method standard
for testing the filtration performance of nonwovens.

v
International Standard ISO 25081:2026(en)
Nonwovens — Test methods for filtration of particulate
matter
1 Scope
This document specifies a method to test filtration performance of particulate matter of nonwovens. This
document is applicable to nonwovens for air filtration.
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.
ISO 139, Textiles — Standard atmospheres for conditioning and testing
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 6330, Textiles — Domestic washing and drying procedures for textile testing
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
aerosol
suspension of solid and/or liquid particulate matter in a gas
[SOURCE: ISO 29464:2024, 3.2.1, modified— without Note 1]
3.2
liquid phase aerosol
liquid particles suspended in a gas
[SOURCE: ISO 29464:2024, 3.2.2]
3.3
solid phase aerosol
solid particles suspended in a gas
[SOURCE: ISO 29464:2024, 3.2.9]
3.4
particulate matter
PM
solid and/or liquid particles
[SOURCE: ISO 29464:2024, 3.2.123]

3.5
count median diameter
CMD
particle size of a particle distribution for which one-half the total number of particles are larger and one-half
are smaller
[SOURCE: ISO 16972:2020, 3.61]
3.6
filtration efficiency
ratio of the difference between the concentration of particulate matter before and after nonwoven filtration
and the concentration of particulate matter before nonwoven filtration
3.7
initial filtration efficiency
filtration efficiency of the nonwoven which is calculated as soon as possible after the start of test
3.8
load filtration efficiency
lowest value of filtration efficiency of the nonwoven in the process of filtration from clean state to when the
filtration of nonwoven reaches a certain dust-hold capacity or a certain airflow resistance
3.9
airflow rate
volume of air flowing through the nonwoven per unit time
3.10
airflow resistance
static pressure difference before and after nonwoven filtration
3.11
initial airflow resistance
static pressure difference of the nonwoven which is calculated as soon as possible after the start of test
3.12
final airflow resistance
static pressure difference of the nonwoven which needs to be replaced or regenerated after filtration
3.13
dust-hold capacity
quality of particula
...