Objective:To investigate whether exothermic sodium acetate mattresses were associated with an improvement in the thermal care of babies <30 weeks gestation between birth and admission to a neonatal unit.Study Design:Analysis of a three case series of babies: the first with traditional thermal care of drying and wrapping in a towel, the second with wrapping in food standard polythene bags and the third with wrapping in polythene bags and nursing on an activated exothermic mattress. The main outcome measure was the temperature on admission to the neonatal unit.Result:There were no significant differences between the groups for gestation and birth weight. Hypothermia was less frequent in the ‘bag and mattress’ group compared with the ‘bag only’ and traditional care groups (26 vs 69 vs 84%, respectively) even though the median time to admission was longest in the ‘bag and mattress’ group (23 min). The proportions of babies admitted with temperatures in the target range of 36.5 to 37.5 °C were 46, 27 and 16%, respectively. Multiple regression analysis showed that use of the mattress raised admission temperatures by 1.04 °C. The median temperature of babies in the ‘bag and mattress’ group was higher compared with the other groups (36.9 vs 36.0 vs 35.8 °C), but significantly more were hyperthermic (28 vs 4 and 0.4%, respectively).Conclusion:Use of exothermic mattresses for babies <30 weeks gestation was associated with a significantly greater proportion of babies being admitted to the neonatal unit with a temperature in the euthermic range, but there was also an increased risk of hyperthermia.