When you submerge the cooling collar in water, the special polymer beads inside the product activate. As the water slowly evaporates, it draws heat from your dog and cools them. Since dogs do not have sweat glands, the cooling collar mimics that process of cooling through evaporation. The cooling collar stays cool for up to 3 days! The cooling collars are made of cotton, and filled with polymer beads. They fasten with velcro.