The Relief-Pak® Cold n Hot® Compress has a comfortable soft fabric that conforms to the curves of your skin. Fabric is gentle on the skin frost-free and washable. Put the pack in microwave or chill in freezer. When heated soothes discomfort from stiff neck backache arthritis sprains and bruises. When chilled soothes discomfort from injury sprains and strains muscle soreness bruises swelling and tension headaches. The non-toxic non-crystallizing gel allows pack to contour and stay pliable when heated or chilled. The pack can be used with standard Velcro hook to hold pack in place. circular - 10 diameter