Grabber Foot Warmers 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.