Durable nylon cover is much more durable than vinyl. Will not dry out or crack like vinyl or polyurethane covers. The durable nylon cover with the high quality gel remains flexible after being in a in a sub-zero freezer over 24 hours. Easy to clean with standard anti-microbial sprays. Gel pack has ability to maintain complete contact with the treated area. Can completely wrap around a 360 degree area. Our proprietary gel stays colder for a longer period of time than other products that use bentonite or glycol formulas.