Waterproofing is a fabric's ability to prevent rain water from passing through. A fabric's waterproofing is determined by measuring its resistance to the pressure exerted by a water column, measured in mm (test based on ISO 811 standard). The higher the pressure, the more waterproof the fabric.
A material with a waterproof rating of 2000mm resists the pressure exerted by 2000mm of water (which roughly corresponds to a 2-hour rain shower).
To determine whether a fabric is breathable, we measure its evaporative resistance (test based on standard ISO 11092).
The lower its resistance, the more the fabric will let water vapour produced by the body escape, and therefore the more breathable it is.
For example: RET < 9 = extremely breathable fabric.
A rating to compare products' environmental impact
A product's environmental impact is calculated for its entire life cycle using various indicators. Products are then given an ABCDE rating to help you easily identify products having the best environmental performance (lowest impact) by comparing different products of the same type (T-shirts, bottoms, backpacks, etc.).
Decathlon voluntarily chooses to display the environmental ratings of its products.
Video with explanations: https://youtu.be/8t63KkRwn_8