This one size fits Most Adults CoolDown Corepak and is our coldest size with full coverage and adjustable straps is very comfortable to wear all day long. Can be adjusted to fit most teenagers and adults. Comes in several colors and has multiple settings. This amazing product Stays Cool all day long! No Refrigeration required! Lowers your surface temperature up to 20+ degrees! Made of durable fabric and is reversible for two color choices. It Can be attached to your car seat or office chair for multiple uses. This is a must have product for your personal temperature maintenance. You can even microwave it! This product will hold heat up to 45 minutes in 40-degree weather maintaining your core temperature. Oh yeah! Last for days!