Simply soak the sheet with warm water until the cells expand to approx. 3/4 inch. (To ensure product durability, keep cells under 1".) Thoroughly dry them off and place in freezer with the cloth side up. The ice sheet will stay frozen up to 1 hour, will stay cold for 2 hours at room temperature and will remain cold for up to 6 hours in the 110% thermal bag (not included). Ice sheets should be inserted with the black side facing you. If the cells shrink and appear flat over time, simply rehydrate as per the instructions above.