It's kind of difficult to put a set time frame on weatherproofing. It really depends on your horse and their environment. I will start by saying nothing is truly "waterproof" which is why we use the term "weatherproof". The rain that we had Tuesday evening with the hail and wind, would have soaked through even the most weatherproof of blankets. Any time it rains that hard the water physically cannot run off the blanket fast enough and will begin to pool in small amounts on the blanket. With prolonged exposure to water, and the water not having anywhere else to go, it will ultimately begin to be absorbed by the blanket.