This specification covers material and dimensional requirements for high-density rubber cellular cushion adhered to carpet, rugs, or various substrates intended for use as a separate underlay. However, this specification does not include requirements for burning characteristics. Material covered in this specification comprises Class A and Class B flexible, cellular, high-density rubber. Tests for compression set, compression resistance or compression force deflection, delaminations strength, tensile strength, and accelerated aging shall be performed and shall conform to the requirements specified.