The invention relates to a kneecap which comprises a binder with a four-layer structure. The outermost layer is a windproof and waterproof layer, a second layer of the binder is a heat insulation layer, the windproof and waterproof layer and the heat insulation layer are connected together by knitting, a third layer of the binder is an aluminum foil layer, the periphery of the aluminum foil layer and the heat insulation layer are connected together by knitting, the innermost layer of the binder is a protective layer, an inner layer of the protective layer close to the aluminum foil layer is connected together with the aluminum foil layer through adhesives, the peripheries of the protective layer, the aluminum foil layer, the heat insulation layer and the windproof and waterproof layer are connected together by knitting, a waveguide tube is arranged at the center of the binder, a fluff area for fixing is arranged at the left end of the outer surface of the windproof and waterproof layer, and a fixing inverted barb area corresponding to the fluff area is arranged at the right end of the outer surface of the protective layer. In general, the kneecap has the advantages of simple structure, heating rapidness and good heat insulation effect.