It is not completely rainproof, but the material is waterproof to a minimum of 10,000 mm hydrostatic head and with a minimum of MVTR of 10,000g/m2/24 hours. This means it should be good for 24 hours in a steady downpour. The material is also very quick drying though, so if it does stop being waterproof, it will dry in no time once you're out of the rain. It is also incredibly lightweight, only weighing 4 ounces.