It is a microcapsules in the fibre which is a functionality fibre which can make the wearer in a constant temperature. When you feel hot, the microcapsules in the fibre absorb your heat and make you feel cool, and the microcapsules become liquid. When you feel cold, the microcapsules in the fibre release the stored heat, making you feel warm, and the microcapsules become solid. Also, due to the regenerated cellulose structure, more ideal humidity regulation characteristics​.