This varies per brand and type of raincoat. Each raincoat or rain poncho states whether the fabric is breathable. Breathability is measured in the number of grams of water that a square meter of fabric allows through during 24 hours. If the raincoat has a water vapor permeability of 5000 grams/m2 per 24 hours, it is very breathable. This means that with these raincoats you can cycle and walk quietly without sweating.