An intercomparison of measurements of the thermal conductivity and thermal diffusivity of two poly(methyl methacrylates) is reported. A wide variety of methods were used: temperature wave analysis, laser flash, transient plane source (Hot Disk), transient line-source probe, and heat flux meter methods. A very good agreement of thermal conductivity results, and separately of thermal diffusivity results, was obtained. Similarly, a good agreement between thermal conductivity and thermal diffusivity results, when converted using specific heat capacity and density values, was also obtained. Typically, the values were within a range of approximately ± 10%. Considering the significant differences between the methods and the requirements on specimen dimensions, the level of agreement was considered to be good.