Permeation, penetration, and degradation — the three words buyers conflate
A chemical glove’s biggest failure mode usually isn’t a hole. It’s a buyer who reads “Type A” as “stronger” and hands out a glove that was never tested against the chemical actually on the task.
The hook: two gloves, one wrong assumption
Two chemical-resistant gloves sit on the same shelf. One is marked Type A. The other, Type B. Ask an EHS buyer which one offers better protection and most will point to Type A without reading past the letter — because “A” sounds like a grade, and grades run in order.
That’s the actual risk in EN ISO 374. Type A and Type B require the identical minimum chemical-resistance performance — the letter counts how many reference chemicals a glove cleared, not how strongly it resists any one of them. A Type A glove never tested against the solvent on your bench offers no more documented protection there than an untested glove does. The standard also bundles three separate material properties — permeation, penetration, and degradation — under language buyers routinely treat as one word.
The decode: three tests, three different failure modes
| Property | What it actually measures | Test method | Reported as |
| Penetration | Physical leakage through pinholes, seams, or porosity — a non-molecular defect | EN ISO 374-2:2019 — air-inflation and water-leak test | Pass / fail — the glove must not leak |
| Permeation | Molecular-level migration of a chemical through intact, defect-free material | EN 16523-1:2015 — breakthrough-time test (chemical detected passing through at a defined rate) | Six performance levels, Level 1 (>10 min) up to Level 6 (>480 min) |
| Degradation | Physical deterioration of the material itself on contact — swelling, embrittlement, hardening, softening | EN ISO 374-4:2019 — puncture-force change measured after 60 minutes’ chemical exposure | Percentage change in puncture force (positive = weaker, negative = harder) |
A glove can pass penetration testing perfectly — zero pinholes — and still fail the job if its permeation resistance is short, or if it degrades and loses puncture resistance mid-shift while technically still “resisting” the chemical. None of the three tests alone tells the whole story, which is why UK HSE’s employer guidance treats breakthrough time, permeation rate, and degradation rating as three separate checks — not one.
The Type letters: a chemical count, not a strength score
| Type | Minimum permeation level required | Minimum chemicals cleared (of 18 reference chemicals) |
| Type A | Level 2 (breakthrough time > 30 min) | 6 or more |
| Type B | Level 2 (breakthrough time > 30 min) | 3 to 5 |
| Type C | Level 1 (breakthrough time > 10 min) | 1 or more |
Three literacy points buyers routinely miss:
Type A and Type B share the same performance bar. Both require Level 2 (breakthrough time greater than 30 minutes) as the minimum. The only difference is how many of the 18 EN ISO 374-1 reference chemicals the glove was tested against and cleared. A is not “more resistant” than B against any chemical both were tested against — it’s simply been tested against more of them.
Each letter names one specific chemical, and nothing else. The 18 reference chemicals each carry a fixed letter under EN ISO 374-1 — A is methanol, K is sodium hydroxide (40%), T is formaldehyde (37%), and so on across the list. A glove’s Type A or
B rating covers only the exact letters printed on its label. Confirm the letter for your actual chemical is present; a high Type with the wrong letters covers nothing at your workstation.
“VIRUS” is a separate certification, not a chemical-resistance upgrade. EN ISO 374-5:2016 governs biological risk independently of the chemical Type system. A glove earns the word VIRUS printed under the biohazard pictogram only after a dedicated challenge test — ISO 16604:2004 Procedure B, a bacteriophage penetration test — with no connection to any chemical letter code. A Type A rating implies nothing about biological protection, and a VIRUS marking implies nothing about chemical resistance.
Reading two real gloves
STEGO’s ChemBlock™ ST-8089 (Chem Shield) carries Type A, letter code AKLNPT — six chemicals cleared: methanol, sodium hydroxide (40%), sulphuric acid (96%), acetic acid (99%), hydrogen peroxide (30%), and formaldehyde (37%) — plus the VIRUS marking. STEGO’s KYNO™ ST-2070LP (Ambi-Fit) carries Type B, letter code KPT — sodium hydroxide (40%), hydrogen peroxide (30%), and formaldehyde (37%) — also VIRUS-marked. Both are CE Category III, the EU’s tier for complex-design PPE requiring notified-body oversight beyond self-declaration.
Set side by side, the pattern is exactly what the standard predicts: ST-2070LP’s three letters are a subset of ST-8089’s six, both meeting the identical Level 2 minimum on the letters they share. Neither ADS states a breakthrough-time figure in minutes — the standard requires publishing only the Type and the letters.
Practical takeaways for an EHS selection review
1. Never read the Type letter as a ranking. A vs. B is a chemical-count difference at an identical performance floor, not a strength difference — check the letters, not just the grade.
2. Match letters to your actual chemical inventory, not the highest Type on the shelf. A Type A glove untested against your specific solvent offers no documented protection against it.
3. Treat VIRUS as its own purchasing requirement. If bloodborne-pathogen exposure is part of the task, confirm the word is present under the pictogram — a chemical Type says nothing about it.
4. Ask about degradation separately from permeation. A long breakthrough time doesn’t guarantee the material stays structurally sound for the full task — request the degradation rating too.
5. For chemical mixtures, plan around the weakest link. Manufacturer data covers pure chemicals only; HSE’s rule of thumb is to select on the mixture component with the shortest breakthrough time, not the average.
Where STEGO fits
STEGO’s ChemBlock™ and KYNO™ Article Data Sheets publish the full EN ISO 374 Type and letter-code panel exactly as certified — no rounding up to a Type the glove didn’t earn, no letters omitted. Reading a chemical glove’s label correctly is step one; matching its specific letters against what’s actually handled on your line is the step most selection reviews skip.
