Unlike other Head Blocks on the market which are brittle or heavy, these Prep Blocks are lightweight and durable.Not only are they made with light weight construction but they can also handle heavy loads and repeated use.The outer skin to this new construction is a chemically resistant plastic that can handle rinsing with solvents & cleaners without damage, so it can be reused and pass OSHA protocols for cleanliness! There are 6 curvatures that give this head block versatility. From hyperbolic to parabolic to elevated, this product allows the control of different sizes of heads at different elevations. 6.25”L x 5”W x 4.25”H