DuraForce Bone. Durable Thick Woven Outer Material Makes this toy thicker and stronger than many multiple layer toys. Great for interactive play with one or multiple dogs. Best for dogs who like to whip their toys and play tug for hours. Floats in water, and its machine washable, (air dry). 2 LAYERS OF MATERIAL Duraforce toys are made with UP TO 2 layers. The exterior mesh is thicker that most multiple layer toys!