Skin to Skin as the Only Warmer: The Ambient-Temperature Floor for Kangaroo Care and the Blanket Layers That Extend It

Kangaroo care — a small infant held skin-to-skin on a caregiver's chest — is used around the world both as a clinical method and, where no warmed cot or incubator exists, as the only warmer available. This paper computes the ambient-temperature floor of the method: the room temperature below which skin-to-skin contact alone cannot hold a small infant in thermal balance, and how far stated blanket layering over the pair extends that floor. The model balances infant metabolic heat (3.0 W/kg) plus conductive gain from a caregiver chest at 36.8 °C across 40% of the infant's surface, against dry losses from the unblanketed head (18% of surface) and the back and limbs (42%), whose insulation rises with blanket layers of stated resistance 0.08 m²K/W each, up to four layers. Without any blanket, the floor is 26.4 °C for a 1.0 kg infant, 25.6 °C at 1.5 kg, 24.9 °C at 2.0 kg, 24.3 °C at 2.5 kg, and 23.3 °C at 3.5 kg. Each layer lowers the floor, with diminishing returns: for a 1.5 kg infant the steps are 3.7, 2.6, 1.9, and 1.5 K, reaching 15.9 °C at four layers. The resulting sizing rule gives layers required as a function of room temperature and weight; it returns failure — no layering up to the stated maximum suffices — below 17.6 °C for a 1.0 kg infant, 15.9 °C at 1.5 kg, 14.6 °C at 2.0 kg, 13.3 °C at 2.5 kg, and 11.2 °C at 3.5 kg. Below those temperatures the method, on these assumptions, cannot hold the infant, and a warmer room or a warmed device is required. The smallest infants are the most exposed at every layering: a 1.0 kg infant needs one blanket layer at 26 °C, where a 2.0 kg infant needs none.