Sand bags are often used in both yoga and pilates for added weight on the legs to help relieve stress on the back and for adding deeper stretch to various positions. Each bag has a durable heavy cotton outer bag with a zipper and a leakproof inner bag that also has a zipper. The outer bag is machine washable. Machine wash cold with like colors, lay flat to dry. The bags come unfilled so different bags can have different amounts of sand added and therefore be used in a variety of ways depending on their weight. By Trademark Innovations.