Measurements have been made of the tear strength of several elastomeric materials under threshold conditions, e.g., in the swollen state and at high temperatures when dissipative contributions to the work of fracture are minimized. The materials studied were Neoprene WRT, BR, SBR, EPDM, and a castable polysulfide material, LP-32. They were crosslinked to different degrees, using a free-radical source, or sulfur, or a metal oxide as the crosslinking reagent. Values obtained for the threshold tear strength were similar in all cases, lying in the range 50–200 J/m2. They appeared to be approximately proportional to E−1/2, where E is the tensile (Young's) modulus of the elastomer, as predicted by the theoretical treatment of Lake and Thomas. Values for networks with polysulfidic crosslinks were significantly higher than with monosulfide or C—C crosslinks, by about a factor of 2. Values for carbon black-filled materials were higher also, by about the same factor, in comparison with the equivalent unfilled materials. These effects are attributed to rupture of labile crosslinks, or bonds to carbon black, prior to main-chain rupture.