RET and MVTR do not describe breathability in the same way. The former expresses resistance to the passage of water vapour; the latter, the amount of vapour transmitted. To compare two jackets, start by checking the test method, the conditions and the material actually tested.
RET: understanding resistance
RET, expressed in m²·Pa/W, measures resistance to evaporation. Under comparable test protocols, a lower value indicates lower resistance to vapour transfer. The ISO 11092 method uses a sweating guarded hotplate; the Hohenstein laboratory describes its application to textiles and material assemblies.
This is still a test result. ISO 11092:2026 specifies that its conditions do not represent any particular comfort situation. A single number is therefore not enough to predict how you will feel during an ascent.
MVTR: understanding vapour transmission rate
MVTR is often given in g/m²/24 h: a mass of vapour per unit area over a given period. Under identical conditions, a higher value indicates more vapour transmitted. However, a different temperature, humidity or method can change the result.
ASTM E96 distinguishes, in particular, between water and desiccant test methods. Its warning is clear: the result of one method under certain conditions cannot predict the result obtained under other conditions. ISO 15496 also notes limitations when comparing methods.
MVTR-to-RET conversion: is it possible?
Do not treat these values as two interchangeable units. Without a documented protocol and conditions, an equivalence such as “this MVTR equals that RET” does not provide a reliable comparison. Nor are two specification sheets listing different numbers enough to rank the jackets.
Before choosing, look for four pieces of information:
- the method and its exact variant;
- the temperature and humidity conditions;
- the sample: membrane alone, assembled fabric or garment;
- the condition tested: new or after care.
If these details are missing, consider the numerical comparison incomplete. Also look at the fit, ventilation openings and the layers you will wear: these are practical criteria to check in the specifications and when trying the jacket on.
Explore further with AYAQ
To understand the difference between breathability and water resistance, see our guide to waterproofness and breathability tests. You can then review the features of our men’s hardshell jackets and women’s hardshell jackets, without assuming performance that is not stated in their specifications.