Fitted with ultra-fine heating elements diffusing constant heat for immediate well-being and an optimal foot temperature; Stick-on Therm-ic topcover for added comfort and refinish Custom, 3Feet and 3D insoles (1 pair); One size, easy to trim; Fitted with Bluetooth technology, you can control remotely the heat settings via your smartphone, using the Thermic Heat Control App; C-pack 1700 B batteries provide up to 17 hours of heat; Suitable for use with Therm-ic C-Pack battery range only