1, the warm-keeping principle of wool vest mainly depends on its material itself. Its fiber structure is hollow and contains a lot of still air, so it can effectively isolate the cold air outside and play a role in keeping warm.

2, down vest: the principle of keeping warm is mainly to reduce the loss of heat by forming an air layer. The fiber diameter of down is smaller, and the air layer inside the down vest is more compact, which can better prevent heat loss.