Foam tends to increase skin temperature because foam materials and the air they entrap tend to be poor conductors of heat. Nicholson et al. determined that the heat transfer characteristic of foam mattresses were less than the normal physiological resting heat losses—up to 244 W/m2 heat loss (Nicholson, 1999). Nicholson also compared the heat transfer rates for mattresses with and without their covers and found rates for mattresses with covers were less by nearly half compared to heat transfer rates for mattresses without covers.