To improve heat transfer, the Medivance Arctic Sun® Temperature Management System (Medivance, Inc., Louisville, CO, USA) features an adhesive, water-conditioned, highly conductive hydrogel pad for intimate skin contact. This study measured and compared the heat transfer coefficient (h), i.e. heat transfer efficiency, of this pad (hPAD), in a heated model and in nine volunteers’ thighs; and of 10°C water (hWATER) in 33 head-out immersions by 11 volunteers.

Volunteer studies had ethical approval and written informed consent. Calibrated heat flux transducers measured heat flux (W m−2). Temperature gradient (ΔT) was measured between skin and pad or water temperatures. Temperature gradient was changed through the pad’s water temperature controller or by skin cooling on immersion.

The heat transfer coefficient is the slope of W m−2/ΔT: its unit is W m−2 °C−1. Average with (95% CI) was: model, hPAD = 110.4 (107.8–113.1), R2 = 0.99, n = 45; volunteers, hPAD = 109.8 (95.5–124.1), R2 = 0.83, n = 51; and water immersion, hWATER = 107.1 (98.1–116), R2 = 0.86, n = 94.

The heat transfer coefficient for the pad was the same in the model and volunteers, and equivalent to hWATER. Therefore, for the same ΔT and heat transfer area, the Arctic Sun’s heat transfer rate would equal water immersion. This has important implications for body cooling/rewarming rates.