A rotary rheometer having a an upper heating/cooling assembly and a lower heating/cooling assembly located opposite one another opposite a sample gap. The lower heating/cooling assembly may comprise a Peltier heater and the upper heating/cooling assembly preferably comprises a heating element that mates with a heat spreader for heating and cooling the area above the sample and providing more uniform heating and cooling across the sample gap while also minimizing any chimney effect within the rheometer and/or providing heating/cooling capability that is insensitive to changes in the gap between an upper geometry and the lower heating/cooling assembly. The upper heating/cooling assembly may further comprise a cooling channel for cooling the upper heating/cooling assembly.