What is the coefficient of evaporative resistance?
Breathability is measured using the Thermal Evaporative Resistance (RET) coefficient. It measures the capacity of a fabric to stop water vapor getting out. The lower this resistance (i.e. the lower the coefficient), the more breathable the fabric! (The test method is defined by the ISO 11092 standard).
How to choose breathable clothing
The RET score uses a numerical index:
- RET < 6: The material is extremely breathable, keeping you comfortable during your most intense physical activities
- RET between 6 & 12: The material is very breathable, making it suitable for moderate efforts
- RET between 12 & 20: The fabric is moderately breathable, and therefore not particularly pleasant to wear during a physical effort
- RET > 20: The fabric is not very breathable and therefore not suitable to be worn during physical exercise
- RET > 40: The fabric is considered non-breathable
You will find this information in the technical characteristics in our product information sheets for our Men's/Women's jackets in particular. It is particularly important to measure the breathability for these products because, generally speaking, the more waterproof a product, the less breathable it is (because of the material or coating used to protect against the rain).
If you want good breathability, you can also choose a product with zipped mechanical vents that you can use to regulate your temperature, in addition to having a breathable fabric:
(NB: some brands may also use the MVTR index. "Moisture Vapor Transmission Resistance" to measure breathability. This index measures the amount of water that a square meter of fabric lets through in 24 hours. The lower this index, the more breathable the fabric. For example, a garment with an MVTR of 5000 will have poor breathability, whereas a garment with an MVTR of 30,000 is extremely breathable).