Ex perimental results are reported for measuring the thermal diffusivity of two polymer species: low density polyethylene (LDP E) and polypropylene (PP). Measurements were taken in unsteady state heat flow conditions around the materials’ melting temperature , using a device specially constructed for this purpose. The experimental results for the sample’s temperature profile (tempera ture gradient product) were adjusted with the theoretical results obtained by solving the heat conduction equation. Diffusivity v alues w ere ⁄ for LDPE and ⁄ for PP. This was pioneering work in measuring this property at high te mperatures in non-stationary state heat flow conditions and should be useful in the search for improving the conditions for p rocessing these materials.