Eleven healthy male subjects slept from 13:30 to 15:30 under ambient temperature and humidity maintained at 29℃ and RH70%, using polyurethane foam mattresses (U) and camel mattresses (C). A polysomnography,skin temperature (Tsk), microclimate, bed climate, and subjective sensations were obtained. The rapid eye movement sleep (REM) in the first hour for the U significantly increased compared to that for the C. The leg, arm, and mean Tsks for the C significantly increased compared to those for the U during the later segment of sleep. The microclimate humidity significantly increased, while the microclimate temperature and bed climate significantly increased during the later segment of sleep. The subjective humid sensation and the requirement for decreasing the mattress temperature significantly increased in U compared to the C. These results suggest that bed mattress material can increase the subjective humid sensation and the requirement for decreasing mattress temperature by 1) increasing the bed climate and microclimate temperature and humidity, and 2) changing the REM distribution.