Hester Dual-sided Temperature Sensing High Elasticity Blue PillowThis is a functional pillow core that can be used all year round and provides suitable temperature for the head. The A side is a white temperature sensing surface with an outer layer of natural cotton fiber and an inner layer filled with energy efficient heating fibers using nano heating powder material. It continuously collects external heat to form a thermal insulation layer, slowly dissipating heat and keeping warm and comfortable for a long time;