• We evaluated the safety of insulating the heads of premature infants in servocontrolled thermal environments. We measured the body temperatures of premature infants (seven in incubators, seven under radiant warmers) before, during, and after application of a headwrap made with an olefin and polyester composite (Thinsulate, 3M Co, St Paul). All infants were tested while abdominal skin temperature was maintained at a constant level by servocontrol. Temperatures of the tympanic membrane, rectum, abdomen, and heel remained constant. The insulated headwrap increased the scalp temperature of incubator infants but not radiant warmer infants. Head insulation reduced variability in scalp temperature for radiant warmer infants. We found no evidence of overheating in these infants.