This is an adjustable 21 in long x 6.6 in wide strap that holds the 5 in x 9 in Portable Warmer. It is versatile, it can strap to your arm or even, your leg. It feels very comfy to users. Great for people who need to free up their hands such as moms, teachers, or people that are on the go. Also, by using the strap it helps decrease the amount of heat loss therefore giving the user a longer time of functional, enjoyable heat. 5 in x 9 in Portable Warmer sold separately.