Abstract: The invention pertains to a method and apparatus for testing the tensile strength of a material, particularly an electrically nonconductive material, at a temperature above ambient temperature. The test method is useful for determining the potential suitability of a material for use as a development medium in a thermal development process for preparing relief printing forms. One embodiment of the method includes mounting the strip between upper and lower chucks of a tensile test machine; positioning a means for generating a hot air stream adjacent the strip so that the stream does not impinge the strip; heating the hot air stream to a predetermined temperature above ambient temperature; repositioning the hot air stream so that the stream impinges the strip; and starting the tensile testing when the hot air stream at the predetermined temperature begins heating the strip.