The total thermal insulation of the new-born baby.

1. One hundred and seventeen healthy new-born babies weighing between 0.9 and 4.8 kg at delivery have been studied during the first ten days of life, and sixteen of these babies have been studied serially for 6 weeks after birth. The babies lay supine in a draught-free environment (air speed 4-5 cm/sec) of moderate humidity. The operative temperature was between 26 and 38 degrees C for the babies who were studied naked.2. Total non-evaporative heat loss was calculated from simultaneous measurements of oxygen consumption, evaporative water loss and the concomitant change in mean body temperature.3. Approximately 10% of the total body surface area was in contact with the mattress or floor. Conductive heat loss accounted for only about 5% of all non-evaporative heat loss when the naked baby was lying on a thick foam mattress, but for as much as 25% when the baby was lying in a water-jacketed chamber with a floor of clear plastic approximately 5 mm thick.4. Insulation to heat loss by convection and radiation varied with environmental temperature. Total specific insulation was low in a warm environment when the naked baby vasodilated, and rose by between 16 and 25% to a maximum in an environment of 31 degrees C. It decreased significantly when the baby became physically active in environments with a temperature less than this.5. Total specific insulation in an environment of 31 degrees C varied with body size: it averaged 0.156 degrees C.m(2).hr/kcal in seven naked babies weighing 0.9-1.2 kg, rose to 0.190 degrees C.m(2).hr/kcal in twelve babies weighing 1.8-2.2 kg, and averaged 0.201 degrees C.m(2).hr/kcal in the thirty-four babies who weighed over 3 kg. Tissue insulation accounted for 23% of this total specific insulation in the smaller babies, and about 28% of the total in babies weighing over 3 kg.6. Clothing ten babies in a vest, napkin and long cotton nightdress increased the total specific insulation by an average of 0.23 degrees C.m(2).hr/kcal.