Heat Packs Large Size (5" x 4") Hand and Body Warmer-12+Hours Heat (10 Warmers) One single heat pack can provide over 12 hours of use without hardening. This product contains moxa(Mugwort) which produces a natural scent.- Just open and shake to heat immediately. Each box of 10 moxa packs comes with one FREE application belt (belt is made of plain material and is adjustable). The most effective temperature is 122~140 degrees Fahrenheit. After opening and activating the heat pack, placing the heat pack in your pocket or under your blanket will allow the heat pack to get hotter. Do not use on bare skin.