Apparatus (2) includes a platform (14) on which is supported, via spaced apart posts (16), a stationary rigid support disc (17). Between the platform (14) and disc (17), plaque holder (18) is rotatably mounted. The plaque holder is arranged to hold a plaque (19) for assessment. The plaque is made by injection molding from a composition comprising a polymeric material and a specific amount of reheat additive(s) and any other additives(s) to be assessed. The plaque holder is arranged to move the plaque relative to the disc (17). In an input position, the plaque holder (18) is arranged directly underneath opening (20). In a measurement position, which is 90° from the input position, there are provided first and second temperature measuring assemblies (24, 26) arranged to measure the temperature of the top and bottom surfaces of a plaque held in the plaque holder. The plaque holder can be rotated through 90° from the measurement position to a heating position, wherein the plaque is positioned directly below a heat lamp. In use, the plaque holder is rotated to the heating position, wherein the plaque is heated by the lamp for a predetermined time. Then the plaque holder is rapidly rotated back to the measurement position, wherein the temperatures of the upper and lower surfaces of the plaque are rapidly measured. These steps are repeated and data recorded to allow reheat and/or other characteristics of the plaque to be assessed over time.