Quick facts
- Absorbency figures on adult briefs and underpads come from at least three different routes: the ISO 11948-1 whole-product test, the evaluation framework in ISO 15621, and a supplier's own in-house method.
- ISO 11948-1 measures the absorption capacity of the absorbent core of a body-worn aid under simple conditions. Its own introduction says the method overestimates what a product holds in use.
- Because the test liquid, the soak and drain protocol, the load applied and the size basis are not printed on the pack, two identical numbers can describe very different products.
- The practical answer is not to pick a bigger number. It is to ask which method produced it, under which conditions, and what the rewet figure is.
Two briefs can both carry "3,600 mL" on the case label and behave completely differently on a resident overnight. That gap exists because "absorbency" is not one measurement: ISO 11948-1 is a single whole-product laboratory method, ISO 15621 is a framework that tells you which method answers which question, and a large share of figures on supplier pages come from methods that are never named at all. This guide sets out what each route actually measures, and ends with a table of the questions to ask before you put two numbers side by side in a tender.
Why can two briefs with the same mL figure behave so differently?
The standard that produces most published figures is honest about its own limits. In its introduction, ISO 11948-1 states that the method "measures the maximum absorption capacity of the absorbing material in the entire urine-absorbing aid", that it "is useful for comparing the performance of products whose absorbing cores are uniform in composition and absorbing properties", but that it "overestimates the amount of urine these products hold in actual use" and "has not been validated for predicting performance of urine-absorbing aids whose absorbent cores are designed to be non-uniform in composition and absorbing properties" (SGS-IPS method summary, ISO 11948-1:1996).
The same introduction lists what it does not model at all: the pressure on the product, the posture of the user (sitting, standing, moving, lying down), the flow rate at which urine is lost, and how well the product is put on. Those are the variables that decide whether a resident wakes up wet.
That is not a theoretical concern. A 2019 laboratory study ran ISO 11948-1 — described there as the Rothwell method — on 12 experimental products whose in-use leakage performance had been established with 55 nursing-home residents. The method "showed good repeatability and reproducibility, and reasonable correlation with in-use data. However, it proved blind to the effects of leg cuffs that conferred measurable benefits in real use. It should, therefore, be used with caution." The authors concluded that a manikin-based absorption-before-leakage method, which correlates better with real use but is harder to reproduce, has potential "to replace or complement ISO 11948-1:1996" (Proceedings of the IMechE Part H, 2019).
The practical reading is simple. A rank order produced by one laboratory method under one set of conditions is a starting point, not a verdict. In-use performance still has to be established in use.
What does the ISO 11948-1 whole-product test actually measure?
ISO 11948-1:1996, Urine-absorbing aids — Part 1: Whole-product testing, sits under ISO/TC 173/SC 3 (aids for ostomy and incontinence). Its scope "specifies a method for determining the absorption capacity of the absorbent core of body-worn urine-absorbing aids" (ISO catalogue entry). The concept is deliberately narrow: it is one physical property of one component class, measured on the whole product.
The principle is short enough to state in full: "The urine-absorbing aid is weighed dry, soaked in test liquid, drained, and weighed wet. Subtraction of the dry mass from the wet mass gives the absorption capacity" (SGS-IPS method summary). Everything a buyer cares about beyond that sentence — how fast the fluid is taken up, how much migrates back to the skin under body weight, how the side cuffs behave when the resident turns — sits outside this method.
On status: the 1996 edition remains published and was confirmed at its last systematic review (stage 90.93, effective 7 June 2023) under ISO/TC 173/SC 3 (BDS project record for ISO 11948-1). The companion part is no longer current: ISO 11948-2:1998, Determination of short-time liquid release (leakage) under conditions of light incontinence and low pressure, is listed as withdrawn (ISO 11948-2:1998). That matters when a specification still references a two-part ISO 11948 series as if both parts were live documents.
What does ISO 15621 add beyond a single test?
ISO 15621 is the piece that most buyers never see. It does not produce a number; it tells you which procedures answer which evaluation question. The current edition is ISO 15621:2026, Absorbent incontinence products for urine, faeces, or both — General guidelines on evaluation, published 18 February 2026 and described by the publisher as applicable "for evaluating absorbent incontinence products for urine, faeces, or both for adults and children", providing "a context for the procedures described in other International Standards and for published testing procedures", with "general factors relating to incontinence products and their usage" also addressed (iTeh catalogue record, ISO 15621:2026).
The previous edition, ISO 15621:2017 (Absorbent incontinence aids for urine and/or faeces — General guidelines on evaluation), is listed as withdrawn with the 2026 edition available as its replacement (ISO catalogue entry, ISO 15621:2017). Any specification that still cites the 2017 edition is citing a superseded document, and any comparison table that mixes figures generated under an older evaluation framework with figures generated under the current one is comparing two different things.
The functional difference for a care home is this: ISO 11948-1 answers "how much can this core hold under simple conditions?" ISO 15621 answers "which measurements should be requested, and how should they be interpreted, for this product and this resident profile?" A tender that only names ISO 11948-1 is asking for one number; a tender that references ISO 15621 is asking for an evaluation.
Table 1 — the routes to an absorbency number, compared
| Route | What it is | What it produces | Conditions fixed by | Typical published unit | What it does not tell you | Current status |
|---|---|---|---|---|---|---|
| ISO 11948-1 (whole-product test) | A single laboratory method on the complete body-worn aid | Absorption capacity of the absorbent core: dry mass taken from wet mass after soak and drain | The standard's soak/drain protocol and test liquid | mL or g per product, sometimes per size | Uptake speed, rewet under load, cuff and fit effects, real-use leakage | Published 1996, confirmed 2023 |
| ISO 11948-2 (short-time liquid release) | A separate part aimed at light incontinence and low pressure | Short-time liquid release (leakage) under defined low-pressure conditions | The standard's protocol | As defined in that part | Anything about moderate-to-heavy products | Withdrawn (1998 edition) |
| ISO 15621 (evaluation framework) | General guidelines on evaluating absorbent incontinence products | Not a number: a context and framework for which procedures to use | Not applicable — it points to other standards | Not applicable | Nothing measurable on its own; it is a routing document | Current edition 2026 (2017 edition withdrawn) |
| Supplier-reported / in-house | A method chosen by the manufacturer or importer, sometimes cited, often not | Whatever the supplier chooses to quote — "max", "up to", a rating word, or a figure with no method attached | The supplier's own procedure | Often mL; sometimes only a rating word such as maximum | Whether it is comparable with anything else on the market | Not a standard; no independent status |
> Column 1 of Table 1 is a description of each route, not a ranking. The point of the table is that only one of these four columns produces a number under a published, reproducible protocol.
Where do published absorbency numbers drift?
Six variables move a figure without changing the product. None of them is printed on a case label.
- The test liquid. Figures are generated with a defined liquid at a defined concentration. A number produced with one liquid is not directly comparable with a number produced with another, and supplier pages rarely state which was used.
- Soak, dwell and drain. How long the product sits in the liquid, and how it is drained, change the retained mass. The ISO 11948-1 protocol fixes both; an in-house method may not.
- Applied load. Absorption capacity measured without a load, and rewet measured with a load, are different properties. Many "max absorbency" figures are unloaded capacities.
- Rewet (fluid released back to the skin). This is measured by separate methods — the 2019 study ran a rewet method based on the Spanish national standard UNE 153601-2:2008 alongside ISO 11948-1 (Proceedings of the IMechE Part H, 2019). A product can hold a lot and give a lot back. Rewet is the number that maps closest to skin condition.
- Size and specimen basis. A per-size figure and a per-range figure are not the same quantity. One supplier may publish the largest size in a range and label the whole range with it.
- Definition of the endpoint. "Absorption capacity", "max absorbency", "up to", and an absorbency rating word are four different kinds of claim. Only one of them is a measurement.
Table 2 — what six suppliers publish, and what is left out
Read on 8 October 2026. Figures are the suppliers' own published statements, reproduced here as claims, not as standard test results. Column 3 records whether the listing names the method that produced the figure.
| Product (supplier) | Published absorbency statement | Test basis named on the listing? | Rewet or retention figure published? | Source |
|---|---|---|---|---|
| CliniEco Night Plus adult briefs (CliniEco Medical) | 5,000 mL+ core, stated as tested per ISO 11948-1 whole-product method with 0.9% NaCl simulated urine | Yes — method and test liquid stated | No | CliniEco product page |
| CliniEco Day Comfort adult briefs (CliniEco Medical) | 3,000 mL core, same stated method | Yes — method and test liquid stated | No | CliniEco product page |
| Abri-Form White Foil Comfort Briefs (Abena) | "Max absorbency up to 3600 mL (122 oz)" | No | No | retailer listing |
| Per-Fit Briefs (Prevail) | "Max absorbency up to 700 mL (25.3 oz)" | No | No | retailer listing |
| All-Through-the-Night Briefs (Tranquility) | Size-by-size figures: 547 mL (XS/Y), 657 mL (S), 812 mL (M) | No | No | retailer listing |
| ProSkin Ultra Briefs (TENA) | "High absorbency" — no figure published | No | No | retailer listing |
| Overnight Briefs (Attends) | "Maximum absorbency" rating word only — no figure published | No | No | retailer listing |
Two things stand out. First, the same product category is described with numbers by some suppliers and with adjectives by others, so a buyer cannot assemble a like-for-like table from pack copy alone. Second, only a minority of listings name the method. A figure without a method is not comparable with a figure that has one — which is the single most useful sentence in this article for a procurement file.
Retailers have partly filled the gap by inventing their own scale. The same listings that publish a millilitre figure also carry rating words such as moderate or maximum. That is a merchandising aid, useful for shelf navigation; it is not a test method and does not convert into millilitres.
How should a care home compare two products fairly?
Request the declaration, not the pack. For each candidate product, ask the supplier to state in writing:
- the method used (ISO 11948-1, another named standard, or an in-house method described in full);
- the test liquid and its concentration;
- whether a load was applied, and how much;
- whether the figure is per product, per size, or the largest size in the range;
- the rewet figure, measured separately, and the method used for it.
Then run the products against each other in use, on the residents who actually use them. The 2019 study is the reason to insist on this: a method with good repeatability in the laboratory still failed to detect the benefit of a design feature that showed up in real use, and the authors recommended that it "be used with caution" (Proceedings of the IMechE Part H, 2019). Laboratory figures shortlist products. In-use trials decide between them.
What should an absorbency clause in a tender or specification say?
A clause that only names a millilitre figure will be answered with whichever number is largest. A clause that names the method and its conditions forces a comparable answer. A workable structure:
- State the method: "Absorption capacity shall be declared in accordance with ISO 11948-1."
- State the liquid and the load, or require the supplier to declare both.
- Require a separate rewet declaration, with its method named.
- Require the figure to be stated per size, not per range.
- Require the declaration in writing, on the supplier's documentation, with the standard edition identified.
- Keep ISO 15621 in the evaluation section of the specification, so the tender says which properties are being evaluated rather than only which number is being compared.
The ISO 15621 framework exists precisely to define the evaluation, and its current edition is the 2026 one (iTeh catalogue record, ISO 15621:2026).
Does Canada require one particular absorbency method?
No Canadian regulation prescribes a bench method for adult absorbency. Products of this kind are Class I medical devices under the Medical Devices Regulations (SOR/98-282), which is a risk classification and a market-authorisation route; it is not a performance test. The ISO documents discussed here are international standards that manufacturers, importers and laboratories use voluntarily, and their figures are declarations rather than regulated claims.
For a Canadian care home the practical consequence is that the absorbency number on a case is a commercial specification. It is worth exactly what the method behind it is worth. That is why the questions in this article are worth more than the numbers.
Sources
- ISO 11948-1:1996 — Urine-absorbing aids — Part 1: Whole-product testing (ISO catalogue)
- ISO 11948-1:1996 — full text view (ISO Online Browsing Platform)
- ISO 11948-1 absorption capacity test summary (SGS-IPS Testing)
- ISO 11948-1 project status record, stage 90.93 (Bulgarian Institute for Standardization)
- ISO 11948-2:1998 — Determination of short-time liquid release (withdrawn)
- ISO 15621:2026 — Absorbent incontinence products for urine, faeces, or both — General guidelines on evaluation (iTeh catalogue)
- ISO 15621:2017 — Absorbent incontinence aids for urine and/or faeces — General guidelines on evaluation (ISO catalogue, withdrawn)
- BS EN ISO 15621:2017 (BSI Knowledge)
- An investigation of laboratory test methods for predicting the in-use leakage performance of urine-absorbing aids in nursing homes (Proc Inst Mech Eng Part H, 2019)
- Retailer product listings and rating words for the products cited in Table 2, read 8 October 2026
The incontinence supply planner runs in the browser, needs no account, and returns a monthly unit count and an indicative CAD monthly cost for a care home of a given size, so the products you shortlist here can be turned into a working par level. For the wider buying picture — case and pack units, storage and restocking — the capacity and purchasing-unit comparison across six suppliers covers the layer below this one.
Ordering for a clinic, a lab or a care home? Wholesale and multi-site ordering covers case pricing and account setup, and the B2B wholesale collection lists the lines stocked for institutional buyers. Reselling? become a distributor.
Related reading
- What does 5,000 mL mean on an adult diaper? Absorbency ratings explained
- Adult brief absorbency ratings: what 3,000 mL and 5,000 mL mean in practice
Frequently Asked Questions
Is a higher absorbency number always the better product?
No. A higher ISO 11948-1 figure means the absorbent core held more test liquid under that method's conditions. It does not tell you how fast the fluid is taken up, how much comes back to the skin under load, or how the product behaves when a resident turns. Rewet and in-use leakage are separate properties, and the method's own introduction says it overestimates what a product holds in actual use.
What is the difference between ISO 11948-1 and ISO 15621?
ISO 11948-1 is a single laboratory test that produces a number: the absorption capacity of the absorbent core. ISO 15621 is a framework of general guidelines on evaluating absorbent incontinence products, and it points to the procedures in other standards. One answers "how much", the other answers "which measurements to use and how to interpret them". The current ISO 15621 edition is dated 2026.
Why do two briefs with the same millilitre rating perform differently overnight?
Because the published figure is a laboratory capacity under one set of conditions, while nighttime performance depends on applied pressure, posture, flow rate, fit and cuff design. A 2019 study found ISO 11948-1 blind to the measurable in-use benefit of leg cuffs, and recommended it be used with caution.
What is a rewet test, and why does it matter more than capacity?
Rewet measures how much fluid travels back out of the product to the skin under load, and it is measured by methods separate from absorption-capacity tests — for example the rewet method based on Spanish national standard UNE 153601-2:2008 used alongside ISO 11948-1 in the 2019 study. A high-capacity product with poor rewet can still leave skin wet, which is the risk factor that matters for skin integrity.
Can I compare an adult brief's figure with an underpad's figure?
Only if both were produced by the same method under the same conditions and both are stated per unit of the same kind. Body-worn aids and underpads are different product forms, usually tested by different routes, and the numbers on the packs rarely identify the method. Treat them as separate procurement categories.
Do suppliers have to state which absorbency test they used?
No. There is no Canadian requirement to publish the bench method behind an absorbency figure, and many listings publish a number or a rating word with no method attached. That is exactly why a specification should require the method, the test liquid, the load and the rewet figure to be declared in writing.
Which ISO 15621 edition should a specification reference today?
The 2026 edition. ISO 15621:2017 is listed as withdrawn with ISO 15621:2026 available as its replacement. Referencing a superseded edition in a tender invites answers that cannot be compared with current declarations.
What is the smallest set of questions that makes two absorbency figures comparable?
Four: which method produced the number; which test liquid and load were used; whether the figure is per size or per range; and what the separately measured rewet figure is. If a supplier cannot answer all four in writing, the two numbers should not be placed in the same column.
CliniEco Medical distributes adult incontinence and facility supplies in Canada under MDEL #35334. Products referenced in the comparison tables are listed by brand for identification only; inclusion is not an endorsement of one product over another.
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