This specification covers thermo-reversible and nonreversible (chemical setting) duplicating materials for use in the dental laboratory. Duplicating materials covered by this specification are classified as Type I - thermo-reversible materials (which includes Class 1 - Hydrocolloidal and Class 2 - Nonaqueous organic thermoplastic) or Type II - Nonreversible (which includes Class 1 - Hydrocolloidal and Class 2 - Nonaqueous organic). ADA20-1972D