Very Warm White Goose Down Filled Adult Mummy Style Sleeping Bag Fit for Winter Thermal 4 Kinds of Thickness Camping TravelWhite goose down filling material, comfortable and keep warm. Down is fluffy, sleeping bag is light, but it's warm. Down is very soft and light. There is a small gap between down and down, which causes the air convection in the sleeping bag to be bad. It can form a layer of insulation layer which is isolated from the outside, so that the outside cold air is not easy to reach the inside, and the inside hot air is not easy to reach the outside, so that