RET (Evaporative Resistance)
RET measures how much a fabric resists the passage of water vapour, tested on a heated plate that simulates sweating skin under ISO 11092. Lower numbers mean more breathable.
RET is the metric W. L. Gore publishes for breathability. It runs in the opposite direction to the g/m2/24h figures most other brands quote, and there is no reliable conversion between the two.
Reading the scale
| RET | Interpretation |
|---|---|
| Under 6 | Very breathable |
| 6 to 13 | Breathable, suitable for active use |
| 13 to 20 | Moderately breathable |
| Over 20 | Low breathability, uncomfortable under exertion |
Remember the direction. A RET of 4 is better than a RET of 12. This trips people up constantly because every other number in outdoor clothing is higher-is-better.
Why it cannot be converted to MVTR
RET is measured on a sweating hot plate under controlled temperature and humidity. MVTR is measured by weighing water passing through a fabric sealed over a cup. They describe related physics through completely different apparatus, and the relationship between them is not stable across different fabric constructions.
Conversion charts exist. They are approximations of something that does not hold, and we do not use them.
What we publish
VEAR has no RET figure, because our shell was tested for water vapour transmission under JIS L 1099 method B-1 instead. That means our breathability number cannot be placed next to a Gore RET value in a comparison. We would rather say that plainly than build a table that implies otherwise.
Related terms
- Waterproof and breathability ratings explained: the full method problem
- MVTR: the other breathability metric
- VEAR lab test results: our JIS L 1099 B-1 figure
- Glossary: all terms