This insole contains tourmaline and can heat up spontaneously, and its main effect is to message your feet and keep warm It may not reach high temperature because it makes people feel uncomfortable Benefits Keep warm and keep healthy Long-lasting effect and durable Wear comfortable and beautiful, does not affect your work study and life; No energy use, reliable and environmentally friendly It is much heat based on products, no external power supply and heat. Material: Cotton, Tourmaline Powder Balls, Far Infrared Balls Color: As shown The picture Size: As shown Package Includes: 1 Pair Shoes Insole Note The color is just for reference. It may be slightly different from the actual item. Please allow size 1-3cm difference due to manual measurement. Thank you!