I tried to solve this problem by covering the sleeping bag with a tyvek,Because tyvek is waterproof and breathable,But because tyvek is so lightweight and easy to shift, it was inspired by the bottomless sleeping bag,Full closure of the foot can better protect the foot sleeping bag, also has the function of positioning,The upper part of the open design only needs to be covered on the sleeping bag, no sense of restraint,It is waterproof while also has a certain heating effect.