ISO 21025:2026

• Abstract:

  This document specifies the test method for evaluating the formaldehyde purification performance of interior wall coatings using the bag method. This document is applicable to the measurement and evaluation of formaldehyde purification performance of various types of interior wall coatings. This document can also apply to other indoor decoration materials with formaldehyde purification performance, such as wallpaper, carpets and decorative panels. Additionally, the method can be extended to the evaluation of the purification performance of other carbonyl compounds, such as acetaldehyde, propionaldehyde and butyraldehyde.

• Status: Published
• Publication Date: 02-Aug-2026
• ICS: 87.040 - Paints and varnishes
• Technical Committee: ISO/TC 35/SC 16 - Chemical analysis
• Drafting Committee: ISO/TC 35/SC 16 - Chemical analysis
• Current Stage: 6060 - International Standard published
• Start Date: 03-Aug-2026
• Due Date: 31-May-2026
• Completion Date: 03-Aug-2026

ISO 21025:2026 is an International Standard from ISO on assessing the formaldehyde purification effect of interior wall coatings by the bag method. It specifies how to prepare coated test panels, expose them to formaldehyde in a sampling bag, measure the concentration change, and calculate initial and long-term purification efficiency. The method also applies to other indoor decoration materials and can be extended to other carbonyl compounds such as acetaldehyde, propionaldehyde and butyraldehyde.

What does ISO 21025:2026 specify?

ISO 21025:2026 specifies a laboratory test method for measuring and evaluating formaldehyde purification performance of interior wall coatings. The same method can also be used for other indoor decoration materials with similar purification claims.

The document is organized into clauses for scope, references, terms, principle, apparatus, reagents and materials, experimental system validation, analysis, sampling, standard test conditions, test procedures, precision, and test report. Annex A gives interlaboratory precision results.

Annex	What it covers
Annex A	Informative results of the interlaboratory test used to assess precision

What are the key requirements of ISO 21025:2026?

ISO 21025:2026 requires the specimen to be prepared from a representative sample and applied to a substrate at the theoretical application amount and method stated by the product manufacturer. This matters because the test is meant to reflect the coating as it is actually used.

ISO 21025:2026 uses a conditioned specimen panel placed in a sampling bag, then challenged with a measured amount of formaldehyde solution. The change in bag concentration is used to calculate purification efficiency, so the result depends on controlled exposure, bag condition, and timing.

Test set-up and system checks

• Sampling bags shall be inert, impermeable, non-sorbing, and at least 50 l in capacity.
• Before testing, bags are cleaned and their natural reduction ratio of formaldehyde is checked.
• Subsequent test steps are carried out only when the natural reduction ratio, E, is less than 25 %.
• Formaldehyde concentration analysis follows ISO 16000-3, although other suitable methods may be used if reported.

These checks matter because the bag itself must not remove too much formaldehyde or distort the result.

Test conditions and procedure

• Laboratory conditions are 23 °C ± 2 °C and 50 % ± 5 % relative humidity.
• Testing is carried out in triplicate, with a blank test for every 10 samples.
• The initial formaldehyde purification efficiency is measured after 24 h exposure.
• If the initial efficiency is below 60 %, long-term testing is not continued.

In practice, this gives a pass-through gate: first confirm short-term performance, then proceed only if the sample is strong enough to justify long-term testing.

Long-term performance and emission check

• Long-term efficiency is assessed after repeated daily formaldehyde challenge for 3 consecutive days and a conditioning period.
• The specimen is then retested to determine long-term formaldehyde purification efficiency.
• After that, the specimen panel is checked for formaldehyde emission, which should be less than 100 μg/m3.

This sequence tells a buyer or lab whether the coating keeps working after repeated loading and whether the panel itself later emits formaldehyde.

What terms does ISO 21025:2026 define?

• Natural reduction ratio of formaldehyde in sampling bag - the percentage drop in formaldehyde concentration in a blank bag over a stated time.
• Initial formaldehyde purification efficiency - the coating panel’s ability to reduce a single formaldehyde challenge under the test conditions.
• Long-term formaldehyde purification efficiency - the coating panel’s ability to keep reducing formaldehyde after repeated challenge.
• Sampling bag - the sealed bag used to hold the specimen and carrier gas during the test.
• Specimen panel - the prepared coated test panel placed in the bag for evaluation.

Who uses ISO 21025:2026?

ISO 21025:2026 is used by coating manufacturers, test laboratories, quality managers, and buyers who need a repeatable way to compare formaldehyde purification claims. It is also relevant to developers and assessors of wallpaper, carpets, decorative panels, and other indoor decoration materials with purification functions.

What changed in ISO 21025:2026 from the previous edition?

ISO 21025:2026 is identified as the first edition.

Which standards are used with ISO 21025:2026?

ISO 21025:2026 names these normative references:

• ISO 1513 - examination and preparation of test samples.
• ISO 15528 - sampling of paints, varnishes, and raw materials.
• ISO 3696 - water quality for analytical laboratory use.
• ISO 16000-3 - analysis of formaldehyde and other carbonyl compounds in indoor air and test chamber air.

Annex A also bases the precision study on ISO 5725-1 and ISO 5725-2.

What does the ISO 21025:2026 document contain?

ISO 21025:2026 contains the principle of the bag method, the apparatus and materials needed, and the full test sequence from bag cleaning to final reporting. It includes the formulas for natural reduction ratio and formaldehyde purification efficiency, plus the procedure for long-term efficiency and the post-test emission check. Figure 1 shows the test equipment arrangement, and Annex A summarizes interlaboratory results used to describe repeatability and reproducibility.

International
Standard
ISO 21025
First edition
Paints and varnishes — Assessment
2026-08
of formaldehyde purification effect
of interior wall coatings by bag
method
Peintures et vernis — Évaluation de l’effet de purification du
formaldéhyde des revêtements muraux intérieurs par la méthode
du sac
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
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
6 Reagents and materials . 2
7 Experimental system validation . 3
7.1 Test equipment .3
7.2 Cleaning of sampling bags .3
7.3 Measurement of natural reduction ratio of formaldehyde in sampling bag .4
8 Analysis of formaldehyde concentration . 4
9 Sampling . 4
10 Standard test conditions . 4
11 Test procedures . 4
11.1 General .4
11.2 Preparation and condition of specimen panel .5
11.3 Measurement of initial formaldehyde purification efficiency .5
11.4 Measurement of long-term formaldehyde purification efficiency .5
11.4.1 Specimen panel saturation test .5
11.4.2 Test on long-term formaldehyde purification efficiency .5
11.4.3 Determination of formaldehyde emission from specimen panel .6
12 Precision . 6
12.1 General .6
12.2 Repeatability limit, r . .6
12.3 Reproducibility limit, R .6
13 Test report . 6
Annex A (informative) Results of the interlaboratory test . 7
Bibliography . 9

iii
Foreword
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iv
International Standard ISO 21025:2026(en)
Paints and varnishes — Assessment of formaldehyde
purification effect of interior wall coatings by bag method
WARNING — The use of this document can involve hazardous materials, operations and equipment.
This document does not purport to address all of the safety problems associated with its use. It is
the responsibility of users of this document to take appropriate measures to ensure the safety and
health of personnel prior to the application of the document, and to determine the applicability of
any other restrictions for this purpose.
1 Scope
This document specifies the test method for evaluating the formaldehyde purification performance of
interior wall coatings using the bag method.
This document is applicable to the measurement and evaluation of formaldehyde purification performance
of various types of interior wall coatings.
This document can also apply to other indoor decoration materials with formaldehyde purification
performance, such as wallpaper, carpets and decorative panels. Additionally, the method can be extended
to the evaluation of the purification performance of other carbonyl compounds, such as acetaldehyde,
propionaldehyde and butyraldehyde.
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 1513, Paints and varnishes — Examination and preparation of test samples
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
ISO 16000-3, Indoor air — Part 3: Determination of formaldehyde and other carbonyl compounds in indoor air
and test chamber air — Active sampling method
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
natural reduction ratio of formaldehyde in sampling bag
ratio of the reduced concentration of formaldehyde in the blank sampling bag to the initial concentration of
formaldehyde within a certain period of time

3.2
initial formaldehyde purification efficiency
ability of the coating test panel in the bag to purify formaldehyde after applying a single specified
concentration of formaldehyde, under the specified test conditions
3.3
long-term formaldehyde purification efficiency
ability of the coating test panel in the bag to maintain formaldehyde purification performance after repeated
application of formaldehyde at a specified concentration, under the specified test conditions
4 Principle
The specimen panel is prepared according to the theoretical application amount and application method
provided by the coatings product manufacturer.
Then the specimen panel is conditioned under standard test conditions for a specific period of time and put in
a sampling bag. A certain amount of formaldehyde solution is injected, or a certain amount of formaldehyde
solution is injected several times until certain saturation state has been reached.
The change of formaldehyde concentration in the bag within a specific period of time is analysed, and the
initial formaldehyde purification efficiency and long-term formaldehyde purification efficiency of the sample
are calculated.
5 Apparatus
5.1 Sampling bag, with the following characteristics:
— material and capacity: the sampling bag material shall be inert, impermeable, and non-sorbing [e.g.
fluorinated resins, such as poly (vinyl fluoride) (PVF) or fluoroethylene/fluoropropylene copolymer
(FEP) plastic]. The bag capacity shall be at least 50 l.
— airtightness: sampling bags shall be sealed securely with low-emitting tape or sealing strip or heat
bonded so as to be isolated from the uncontrolled ambient air.
— background concentration: the background concentration shall be as low as possible (e.g. below 7,5 µg/
m for formaldehyde) so that it does not interfere with the test results.
5.2 Micro syringe, with a volume of 10 μl and division value of 0,2 μl.
5.3 Sampling pump, which shall meet the requirements of ISO 16000-3. The flow shall be stable during
the sampling process. The flow range shall be 0 ml/min to 1 200 ml/min, and the flow fluctuation shall not
exceed ± 5 % of the sampling flow. Gas flow meters should be regularly used to calibrate the sampling pump.
5.4 Gas mass flow controller for filling the sampling bag with carrier gas. The response time should be
less than 100 ms and the repeatability should be ≤ 0,1 % (full scale). Gas flow meters should be regularly
used to calibrate gas mass flow controllers.
5.5 Vacuum pump, empty the gas in the sampling bag quickly.
...