This specification covers preformed open-cell sponge rubber gaskets, for use in new or reconditioned pails or drums, of the following classes: Class A and Class B, each divided into Grade 1, Grade 2, and Grade 3. Cellular sponge rubber gaskets shall be made by incorporating a blowing agent into the compound, such as sodium bicarbonate, that gives off a gas which expands the mass during the vulcanization process, and shall be manufactured from natural rubber, synthetic rubber, or rubber-like materials, together with added compounding ingredients. Unless otherwise specified, gasket sponge rubber shall have a natural skin on both the top and bottom surfaces. Cellular rubber shall conform to the prescribed requirements as to physical properties such as (1) compression at deflection, (2) change in volume upon oil immersion, (3) change in compression value after heat aging, (4) compression set, and (5) color (tan or black). The following test methods shall be used: (1) compression deflection test, (2) oil immersion test, (3) heat oven aging test, and (4) compression set test under constant deflection. The formula for calculating the compression set is given. The requirements for sampling, test specimens and slabs, and measurements of test specimen such as width and thickness are detailed as well. The location from which standard test specimens are to be cut when testing standard test slabs or commercial flat sheets and the four-cavity frame for standard test slabs of cellular rubbers are illustrated.