Beyond Absorbency: PHMB Foam Dressing Performance Metrics for Distributors

A supplier’s absorbency or MVTR figure cannot go into a comparison column until its annex, test fluid, conditioning, orientation and units are known. EN 13726:2023 supplies test methods, not pass/fail limits, so two numbers that look alike can describe different tests. This guide gives distributors a fixed reporting template and a metric set to request from any PHMB foam dressing supplier.

Two limitations apply throughout. First, MVTR values cannot be compared across dressings unless the complete method is identical, so no cross-configuration ranking is offered here. Second, PHMB antimicrobial performance is a separate evidence set from physical fluid management and is reported separately.

This is a benchmarking framework, not clinical guidance. It tells you what to ask for and how to read the answer.

Key Takeaways

• EN 13726:2023 defines test methods, not pass/fail limits, so a supplier’s figure is only comparable when its annex, test fluid, conditioning and units are stated.

• Four fluid metrics exist (free-swell absorbency, fluid retention, absorption under compression, fluid handling capacity), and they answer different questions.

• MVTR is configuration-dependent: the same seven dressings produced a 36-fold spread between upright and inverted testing.

• PHMB antimicrobial evidence is a separate set from physical fluid management and should never be summed into the same column.

What does EN 13726:2023 cover, and which annexes apply to foam dressings?

EN 13726 test methods for wound dressings were consolidated in 2023, when the 2023 edition replaced the four former parts. EN 13726:2023 supersedes EN 13726-1:2002, EN 13726-2:2002, EN 13726-3:2003 and EN 13726-4:2003, merging them into a single standard (SIST EN 13726:2024, retrieved 2026-06-11). The Estonian standards record dates publication to 2023-09-20, with the four 2002 and 2003 parts withdrawn from 2023-10-02, so the 2023 edition has been in force since October 2023 (EVS, retrieved 2026-06-11).

The scope is narrower than the title suggests. The standard specifies test methods for absorption, moisture vapour transmission, waterproofness and extensibility, and it defines methods, not pass/fail limits (SIST EN 13726:2024, retrieved 2026-06-11). A supplier cannot claim a dressing “passes EN 13726” in the way a product passes a safety threshold.

The annex map for foam dressings is the practical starting point.

The standard’s own reviewers note that the informative annexes carry limited weight. Nygren and Gefen describe a two-tier structure in which normative annexes B, E, F, G, H, I, J and K are well-established protocols, while informative annexes C, D and O provide supplementary guidance whose applicability is constrained by a lack of round-robin validation (International Wound Journal, 2024). Annex A of the standard itself concedes that inter-laboratory experiments showed unexplained variation, especially between laboratories.

That gap matters commercially. An accredited UK laboratory lists Annexes B, C, D, E, N, O, F, G, H, I, J and K among its wound-dressing methods under UKAS accreditation (NHS Wales SMTL, retrieved 2026-06-11), so an accredited report can rest on methods the standard labels unvalidated. Ask which annex each number came from before it enters a comparison.

What is the difference between free-swell absorbency, fluid retention, absorption under compression, and fluid handling capacity?

Absorption under compression wound dressing metrics split into four distinct measurements, and each answers a different procurement question. Free-swell capacity is the total absorptive capacity in excess test liquid with no applied load, reported in g per complete dressing and g/cm² of absorbent area for intact dressings, g/cm² for sectioned sheet dressings, and g/g for rope or ribbon cavity dressings (SIST EN 13726:2024, retrieved 2026-06-11).

Retention is measured after a specified temporary compressive load, reported as g per intact dressing, g/cm² of absorbent area, and percentage of fluid retained (SIST EN 13726:2024, retrieved 2026-06-11). Absorption under compression reverses the sequence: liquid is absorbed while the dressing is already under compression, reported as g/cm² of absorbent area, and an accredited laboratory confirms it runs Annex D (NHS Wales SMTL, retrieved 2026-06-11). Fluid handling capacity combines absorption and moisture vapour loss over 24 hours.

The failure mode is treating these as interchangeable. The standard admits that the Annex B to E tests use fully saturated dressings, “which is rarely the clinical situation,” because most dressings leak long before saturation and are changed earlier. A high Annex B number therefore describes a state the dressing rarely reaches.

Why can two dressings’ MVTR numbers not be compared directly?

MVTR wound dressing testing produces configuration-dependent numbers, so a higher figure does not mean a better dressing. MVTR is reported in g/m²/24 h with the contact configuration named, and the two EN 13726 configurations are vapour contact (upright cup) and liquid contact (inverted cup) (Journal of Vascular Access, 2021).

The scale of the difference is the point. Across seven IV dressings, vapour-contact MVTR ranged 773 to 2,838 g/m²/24 h while liquid-contact MVTR ranged 845 to 30,530 g/m²/24 h, so the same seven dressings produced a 36-fold spread between the two configurations (Journal of Vascular Access, 2021). The study tested IV dressings, not foams, so the range should not be generalised to all foam products.

The two configurations measure different things. Vapour-contact testing separates the dressing from the liquid by an air gap and characterises the backing film under drier conditions, while liquid-contact testing wets the wound-facing side directly and reflects the whole wet construction under heavy exudate (Journal of Vascular Access, 2021). A dressing with a highly permeable backing can score well upright and poorly inverted, or the reverse.

MVTR values are not directly comparable unless the complete method is identical: contact configuration and orientation, test liquid, temperature and humidity, duration, exposed area, and whether the dressing is allowed to swell. The two methods did not consistently rank dressings the same way (Journal of Vascular Access, 2021). Cross-study variation confirms this: the same foam dressing has been reported at roughly 11,400 and 12,000 g/m²/24 h in different studies, another at 4,170 and 5,500, and a third at 1,730 and 1,100 (International Wound Journal, 2014).

Two further artefacts corrupt reported values. The standard’s Annex A describes high-MVTR dressings creating a partial vacuum that distorted the dressing and caused inverse doming, resolved by a vented lid with a 0.25 mm hole and bolts tightened to 2 Nm torque (SIST EN 13726:2024, retrieved 2026-06-11). The 2021 study independently observed concave deformation from a vacuum in both cup orientations and found the test cup empty at the end of one inverted test, making that value questionable (Journal of Vascular Access, 2021).

There is also a unit conflict to resolve. The standard defines MVTR as g/cm²/24 h of the absorbent area, while the 2021 study reports g/m²/day. The standard is the authoritative unit definition for compliance claims; the study is the more informative source on method-dependence.

How does compression therapy change measured dressing performance?

Compression changes both the fluid a dressing can hold and the fluid it can take up, so off-load laboratory numbers overstate real performance. In a robotic leg-ulcer model, one multi-layer foam retained about 80% of simulated wound fluid with no spillover, while a foam-border dressing showed 5-fold greater cavity fluid and 4% spillover at 24 hours (International Wound Journal, 2023).

The retention loss on a posture change is measurable. In a diabetic-foot-ulcer phantom, a CMC-based dressing pair lost 13% of retention on a supine-to-standing transition (82 ± 3.8% standing versus 95 ± 2.1% supine), while a PVA-based pair retained 97.3 ± 2.3% standing (International Wound Journal, 2022). The authors attribute the drop to the simulated bodyweight reducing the pair’s retention reservoir, which in practice represents getting out of bed.

Swelling is the mechanism. Foam dressings increased up to 30% in size after absorbing saline, so under a compressive dressing they may not reach their absorptive capacity (Advances in Wound Care, 2021, citing Salmerón-González et al. 2018). A dressing that cannot expand cannot use the capacity its Annex B number promises.

Two caveats keep this honest. The simulator studies are laboratory models, not clinical trials, and they list their own limitations: no mixed-aetiology ulcers, no paediatric legs, static standing only, and fluid delivered from an external reservoir rather than from oedematous tissue. The 10 to 20 mmHg peri-wound pressures reported in the VLU model are not established as occurring in real patients. The VLU study also notes that leg-ulcer exudate may be highly viscous, and a non-viscous test fluid cannot discriminate between dressings whose differences emerge only with viscous fluid.

How should PHMB antimicrobial performance be reported separately from physical fluid management?

PHMB antimicrobial performance belongs in its own evidence column, because the method and the conditions differ from every fluid metric above. PHMB is a cationic antimicrobial polymer that binds negatively charged bacterial surfaces, disrupts membrane permeability causing leakage of potassium and cytoplasmic contents, and can bind or condense DNA, with reported activity against Gram-positive and Gram-negative bacteria including MRSA, selected fungi and biofilms (GMS Hygiene and Infection Control, 2024).

The in-vitro numbers are strong but narrow. Irrigation solutions containing 0.1% PHMB achieved more than a 4-log reduction against planktonic cultures within 60 seconds, and all tested irrigation solutions showed at least 3-log reduction of ESKAPE microbes, though with dramatic differences in the time required (GMS Hygiene and Infection Control, 2024). That study concerns surgical irrigation, not wound dressings, so it establishes the agent’s in-vitro behaviour, not a dressing’s clinical effect.

Clinical evidence is weaker and mixed. One trial found a significant decrease in bacterial count at 60 minutes after polyhexanide versus baseline but no significant difference versus Ringer solution, and healing results across trials were mixed with no significant difference versus saline (NCBI Bookshelf, 2023). NICE found little high-quality trial evidence that antimicrobial dressings prevent infection, and the VULCAN trial (n=213) showed no significant difference in median time to complete healing or healing rates at 3, 6 and 12 months (NICE ESMPB2, 2016). NICE’s summary does not mention PHMB specifically, so it cannot be cited as a PHMB finding.

One antimicrobial dressing does carry high-quality evidence, and it is not PHMB. Chlorhexidine-impregnated dressings are the exception, with four low-risk-of-bias trials suggesting a benefit in reducing catheter-related bloodstream infection (CDC, 2024). That finding should not be generalised to PHMB or silver.

The reporting rule follows. Log reduction is an in-vitro result, not clinical infection control, and it must never be summed with fluid-handling metrics into a single performance score. Record the agent, the concentration tested, the organisms, the contact time and the method, and keep the column separate. Where a product’s PHMB concentration is not published, the template should record “not stated” rather than leaving the field blank or inferring a value.

Which usability KPIs should a benchmarking pack track?

Wound dressing usability KPIs should be requested as measurement definitions, because no published benchmark values exist for most of them. The clinical study read for this framework reports investigator ratings such as “good” or “very good” and a distance-to-edge comparison rather than failure rates, and the qualitative interview study reports themes rather than numbers. A distributor should therefore specify what to measure and how to report it, not expect a market benchmark.

Two evidence points shape the request. Wear time depends on absorptive capacity and structural integrity: a dressing is replaced when it reaches capacity or when the adhesive fails at an edge, and foam dressings are commonly left in place for two to three days (Advances in Wound Care, 2021). That makes wear time a function of both the fluid metrics and the adhesion system, so the two should be reported together.

The second point is that laboratory discrimination is not clinical superiority. NICE’s summary of Cochrane reviews reports no statistically significant healing differences for alginate versus hydrocolloid versus non-adherent dressings, or across foam comparisons, with evidence quality rated very low to low (NICE ESMPB2, 2016). Usability KPIs are therefore operational measures for tender evaluation, not proxies for healing outcomes. For how usability behaves on a contoured anatomical site, see silicone foam dressings for the sacrum.

What evidence should a distributor request from a supplier in a tender?

A supplier qualification pack should be requested as a fixed document list, because incomplete test reports are the most common tender problem. The qualification pack a distributor should request covers four groups: the declaration of conformity and its standard list, the quality management certificates, the test reports with full method statements, and the batch-release records.

The standard’s own rationale supports this level of scrutiny. Annex A notes that European procurement legislation has changed and it is increasingly common for contracts to specify that data be provided in compliance with EN 13726, while the technical issues inherent in the standard mean the usefulness of some of that data is questionable and can be misleading (SIST EN 13726:2024, retrieved 2026-06-11). A tender that specifies EN 13726 compliance is therefore specifying a method, and the report has to be read as a method statement.

Two report-level checks catch most problems. The standard requires that any deviations from its test parameters be validated by the laboratory undertaking the test and noted in the test report, so a report without a deviations section is incomplete. And because the 2021 study’s own protocol deviated from the standard on temperature, aperture and fluid volume while arguing the deviations do not change the normalised result, the validation record is the only way to reconcile the two positions. For how a supplier’s quality system supports batch-level reliability, see ISO 13485 and medical dressing reliability.

How do you build a reporting template that keeps PHMB foam dressing performance metrics comparable?

A comparable PHMB foam dressing performance metrics template works by fixing the fields before the numbers arrive. Every metric row carries the same eleven fields, and a number without all eleven is not comparable.

The individual-results and standard-deviation fields address batch-to-batch inconsistency directly. A mean alone hides the spread that a distributor needs to assess, and the standard’s own Annex A flags inter-laboratory variation as the reason two annexes are informative.

The template should also record what the evidence does not cover. No source in this framework provides clinical outcome data for the specific dressings named in the laboratory studies, and no source reports results from a more biologically representative simulated wound fluid, so the template should not invite a clinical claim. The standard’s Annex Q leaves space for substituting Solution A with more representative fluids, but the effect of that substitution is not yet reported.

A worked example makes the template concrete. A PHMB foam dressing with a polyurethane film backing, a PHMB-containing foam layer and a silicone contact layer would be entered as three rows: Annex B free-swell, Annex E fluid handling capacity, and a separate antimicrobial row recording the agent, the concentration tested if stated, the organisms, the contact time and the method. The antimicrobial row is never summed with the fluid rows. For how factory quality control supports this level of reporting, see medical dressing factory QC.

Frequently Asked Questions

Can I compare two suppliers’ absorbency figures directly?

Only if the annex, standard edition, test fluid, conditioning, orientation, duration and units are identical. Free-swell absorbency is reported in g per dressing and g/cm² of absorbent area, while fluid handling capacity is reported in g/cm² over 24 hours (SIST EN 13726:2024, retrieved 2026-06-11). Two figures in different units are not comparable, and a higher number is not automatically better.

Is a higher MVTR always better?

No. MVTR is configuration-dependent: across seven IV dressings, vapour-contact values ranged 773 to 2,838 g/m²/24 h and liquid-contact values ranged 845 to 30,530 g/m²/24 h (Journal of Vascular Access, 2021). The two methods did not consistently rank dressings the same way, so a higher figure reflects the test, not necessarily the product.

Does EN 13726:2023 certify that a dressing works?

No. The standard specifies test methods and defines no pass/fail limits (SIST EN 13726:2024, retrieved 2026-06-11). Compliance means the method was followed, and the report still has to be read for annex, conditions and deviations.

Can a PHMB dressing claim to prevent infection?

Not on the evidence here. In-vitro testing shows more than a 4-log reduction within 60 seconds at 0.1% PHMB (GMS Hygiene and Infection Control, 2024), but NICE found little high-quality trial evidence that antimicrobial dressings prevent infection (NICE ESMPB2, 2016). Log reduction is an in-vitro result, not clinical infection control.

Conclusion

A defensible comparison rests on method disclosure, not on the size of a number. EN 13726:2023 gives distributors a common set of test methods, and the annex map, the four fluid metrics, the MVTR configuration rule, the compression correction and the separate PHMB evidence column together form a framework that can be applied to any supplier’s pack.

The next step is to send the eleven-field template to each supplier and ask for the completed rows, with individual results, standard deviations and any deviations from the standard. A supplier whose evidence system can fill every field is a supplier whose numbers can be placed in a comparison column. To start that process, request the specification sheet, instructions for use, certifications pack and sampling plan.