To find out if a fabric is breathable, we test its evaporative resistance RET (ISO 11092 standard).The lower the fabric's resistance, the more water vapour evaporates, and the higher the fabric's breathability.
It is considered that if:
RET <9 = very breathable fabric
9< RET <12 = breathable fabric.
Here are the breathability values for the Trek 500 over-trousers:
> Most durable fabric:RET<12 (or 3,621 g/m²/24h, standard JIS1099A)
>Lightest fabric: RET <8 (or 2,972 g/m²/24h, standard JIS1099A)