The Grabber Foot Warmers ultra thin warming insole will keep your feet toasty for over five hours. Patented technology allows the warmer to do extremely well in low oxygen environments such as shoes or boots. The warmer is odorless, clean, dry, non-toxic, non-flammable, and biodegradable. No shaking or cutting required; simply open package and insert insole into shoe or boot for all day warmth. Grabber Warmers is a recommended product by the National Ski Patrol. Foot Warmers are great for travel, cycling, snow sports, camping, fishing, hunting, and spectator sports. Also great for relieving pain associated with arthritis and poor circulation.Ultra thin, full foot warming insole. Two sizes available: Small/Medium (women's shoe size 5-8; men's size 4-7). Medium/Large (women's shoe size 9 and above; men's size 8 and above). Small/Medium (women's shoe size 5-8; men's size 4-7). Medium/Large (women's shoe size 9 and above; men's size 8 and above). Lasts 5+ hours. Pack weight: 1.6 oz. Average temperature when activated 95? F. One pair per pack (2 warmers).