Cold-water diving requires good thermal insulation because hypothermia is a serious risk. Water conducts heat more efficiently compared to air. To stay warm during a dive, the choice of thermal protection should be based on physical activity, the temperature of the water, and the duration of exposure. A dry suit, a diving suit filled with gas, is the most common diving suit in cold water. Air is the traditional dry suit inflation gas, whereas the thermal conductivity of argon is approximately 32% lower compared to that of air. This study evaluates the benefits of argon, compared to air, as a thermal insulation gas for a dry suit during a 1-h cold-water dive by divers of the Royal Netherlands Navy. Seven male Special Forces divers made (in total) 19 dives in a diving basin with water at 13 degrees C at a depth of 3 m for 1 h in upright position. A rubber dry suit and woollen undergarment were used with either argon (n = 13) or air (n = 6) (blinded to the divers) as suit inflation gas. Core temperature was measured with a radio pill during the dive. Before, halfway, and after the dive, subjective thermal comfort was recorded using a thermal comfort score. No diver had to abort the test due to cold. No differences in core temperature and thermal comfort score were found between the two groups. Core temperature remained unchanged during the dives. Thermal comfort score showed a significant decrease in both groups after a 60-min dive compared to baseline. In these tests the combination of the dry suit and undergarment was sufficient to maintain core temperature and thermal comfort for a dive of 1h in water at 13 degrees C. The use of argon as a suit inflation gas had no added value for thermal insulation compared to air for these dives
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