Water has a 25 times higher thermal conductivity than air. Water removes more heat from the body compared to air. Wet or dry suits are used to protect against hypothermia. The thickness of wetsuits ranges from 2 mm up to 8 mm. The insulating effect is based on tiny air pockets in the rubber. A thin layer of water sits between skin and neoprene, which is heated up by the body. The water film is merely exchanged and remains stationary. As a result, convection is reduced and body heat is preserved. Convection is the process of enhanced heat transfer to another medium that has a different temperature. It can add or remove heat from one medium to the other. The water layer under the neoprene has usually only little exchange with water of the environment. If however the wetsuit is too big, the gap widens between the skin and neoprene, which facilitates the exchange of the already heated water under the neoprene and the cold water of the environment. This causes further heat loss. The insulating effect is decreasing with increasing depth as air bubbles in the neoprene become smaller, which decreases its insulating effect. Dry diving suits prevent the diver’s skin from any direct contact with water at all. The insulating effect is caused by warm clothing under the dry suit and the reduction of conduction. To maintain neutral pressure within the dry suit, air needs to be supplied and released to inside of the dry suit. Unlike the neoprene suit, the dry suit is a closed system and does not have direct exchange with the environment. This results in less heat loss due to convection. The insulating effect is better in dry suits than in wetsuits. To avoid hypothermia during diving, the head should be covered as well. As skin vessels of the scalp have limited ability to contract, body heat can be lost significantly. At lower water temperatures, gloves and boots should be used as well, to minimise the area of convection.
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