* "Z" Blocks have 3 corrugated surfaces that indicate the areas where one sits. ** "Z" Blocks are made out of polystyrene foam. Polystyrene is a colorless, rigid and economocal plastic that can easily be returned to a liquid by heating and used again for molding or extrusion. It is light-weight material - about 95%air, that also exhibits good damping properties. The blocks have a protective coating in the form of a transparent adhesive and a silicone outer layer, that protect them against coronation. It is degradable.