Water conducts body heat away from the body faster than air by what factor?

• A. 5 times
• B. 10 times
• C. 25 times
• D. 50 times

Answer: (C)

Water pulls heat from the body much faster than air because its ability to conduct heat is far greater. The typical figure used is about twenty-five times faster. This comes from the thermal conductivities: water around 0.6 W/mK versus air around 0.024 W/mK, so roughly a 25-fold higher heat transfer capability. With skin in contact with water, heat transfer happens via conduction and is enhanced by convection as the water moves, producing a heat loss rate about 25 times that in air for the same temperature difference. In practical terms, cold water can drain body heat far more quickly than cold air. Thus the widely cited estimate is twenty-five times. The other numbers would understate or overstate the actual difference and don’t align with the material properties involved.