Abstract A new apparatus is described whereby the thermal behavior, including the deformation temperature, of a thermoplastic material may be obtained. The apparatus is intended to replace ASTM procedure No. D648‐56 and has several advantages over that procedure. Thermal behavior of several common thermoplastics under two different stresses and for three different heating rates is described. An application to the determination of optimum cure times for certain thermosetting epoxides is also described.