Carried Against the Body: A Heat-Balance Bound for Cloth-Wrap Carrying by Climate

Carrying an infant in a cloth wrap against the caregiver's body is the default transport and soothing method across much of the hot world, yet there is no simple statement of how long it can continue in a given climate before the infant's body begins to store heat. This paper computes one. A coupled heat-balance model — infant metabolic heat production, conductive exchange with the caregiver's torso across the contact area, dry losses through the wrap and from bare skin, and humidity-limited evaporation capped by an immature sweating capacity — is evaluated for infants of 4, 7, and 10 kg, front and back carrying, seated and walking caregivers, and ambient temperatures from 20 to 40 °C at 40% and 70% relative humidity. Storage is charged against a stated margin equal to a 1.0 K mean body-temperature rise (24.3 kJ for the 7 kg reference infant). For a walking caregiver carrying a 7 kg infant in front at 70% humidity, the maximum continuous carrying duration falls from 59 minutes at 25 °C to 29 minutes at 30 °C, 19 minutes at 35 °C, and 14 minutes at 40 °C; at 40% humidity the same durations are 96, 39, 24, and 17 minutes. Back carrying buys a few minutes at moderate temperatures (59 versus 52 minutes at 28 °C, dry air, walking) and nothing at 38–40 °C. Unwrapped rest in shade removes a full margin of stored heat in 9 minutes at 25 °C and 70% humidity, 17 minutes at 30 °C, and 30 minutes at 32 °C — but at 70% humidity and 35 °C or above, an unwrapped 7 or 10 kg infant in this model cannot shed heat at all, so no carrying duration is safe without moving to cooler air or active cooling. At 40% humidity that failure point is 40 °C. Larger infants reach the margin sooner than smaller ones at the same climate, because metabolic heat scales with mass while surface area does not.