Our Crystal Cold Packs are constructed from a durable twill material and designed with pockets that hold tiny crystals. The crystals within the pockets are capable of expanding to 10 times their size when immersed in cold water. You must soak crystals in water to activate them. Will remain cool for 1 - 2 hours. After use, lay flat or hang to air dry and crystals will return to original state. Our Crystal Cold Packs are an excellent cooling therapy for horses legs and can be used over and over. Sold per pair. (may also be soaked in warm water for heat therapy if needed).