This specification covers sheet and tubular preformed flexible elastomeric cellular thermal insulation. The materials are classified into three grades according to the operating temperature range of the industrial systems that each material is used for. The non-thermoplastic, thermoset products should be made of natural or synthetic rubber that may be modified using various thermoplastic or thermosetting resins, plasticizers, modifiers, antioxidants, curatives, blowing agents, and other additives. All products should be tested using the prescribed procedures and conform to the specified values of apparent thermal conductivity, water absorption, water-vapor permeability, and linear shrinkage.