these are the soothing insulated slippers with three heat settings to keep feet toasty inside the home or outside around the fire pit on frosty evenings. After sliding your feet into the cozy fleece interior, the interior temperature can be set (by a button on each battery pack) to low, medium, or high to bathe the toes in luxurious warmth. A timer automatically shuts off the heating elements after 60 minutes. The anti-slip soles assure a good grip indoors or out, and the waterproof 100% polyester exterior provides a barrier against the elements to keep feet dry. Each recharges in three hours using the included USB charging cord. Sizes M (Women’s 6 1/2-8), L (Women’s 8 1/2-10); Men’s 7-8 1/2), and XL (Women’s 10 1/2-12; Men’s 9-10 1/2).