I went to a winter mountain school with this membrane. 5 days, 3 peaks. It was tested in extreme conditions in Dirfi, especially for Greek standards. It doesn't let anything through, not air or water. Perfect in every way. Obviously, it needs another layer of clothing like fleece to keep warm in very cold weather, as it is a membrane and not a jacket. It would be even better if it had ventilation zippers on the sides. Overall, 5/5!