The variability within the results presented from the guarded hot-plate (GHP) and guarded heat-flow meter (GHF) methods was determined. Multiple thermal properties of polymethyl methacrylate (PMMA) were analyzed to compare methods. These measurements are taken in the range of −70◦C and +80◦C. Providing reference data for PMMA is the main objective of this paper as well as quantifying the effects of thermal contact of the measuring instruments....