Methods and combinations of mattress support surfaces comprising one or more flexible polyurethane foam layers containing highly thermally-conductive solids, such as diamond or silicon carbide, and said layer combination is capable of transferring heat from a warm surface, such as a person sleeping on a bed, to a cooler region at a faster rate throughout the mattress than the thermal dissipation rate obtained from flexible polyurethane foam without highly thermally-conductive solids.