Underwater heat loss occurs approximately how many times faster than in air?

• A. 4
• B. 25
• C. 10
• D. 2

Answer: (B)

When a body is in water, heat leaves much faster than in air because water transfers heat away through conduction and convection far more efficiently. Water’s thermal conductivity is about 25 times that of air, and its greater density makes convection around the body much more effective at carrying heat away. So the rate of heat loss in water is roughly 25 times faster than in air, which is why divers feel cold quickly in cold water and why insulation is so important. The other options underestimate the difference; 25 is the commonly cited factor based on these heat-transfer properties.