The mercaptan rubber should be used for the impression when making indirect single and multiple tooth restorations. For the impression of the full crown preparation, the use of a tube is often the method of choice, but the tray technique is advocated for other types of preparations. Accurate results can be expected if the basic properties of the materials used are understood and correlated with practical application. Rigidity, stability, and a rubber adhesive must be provided in the tray or tube. When the tray method is used, a uniform 2 or 3 mm. thickness of rubber is recommended; also, a double mix technique utilizing a syringe is advised, and the surfaces to be impressed should be exposed to view and dry. Mixing of the base and accelerator pastes must be thorough. Care must be exercised to allow for the development of sufficient elastic property before withdrawing the impression. The impression should be poured as soon as practicable, preferably within a few hours, but if the taper of the preparation is not minimal, a day or two delay is allowable. Two pours are permitted in the tray impression, and any one of several methods may be employed to make the first pour a split model, where desired. A strip method is recommended.