Still water (without currents or convection) conducts heat away from the body by pure thermal diffusion, approximately 20 to 25 times more efficiently than still air. Water has a thermal conductivity of 0.58 Wm−1K−1 while still air has a thermal conductivity of 0.024 Wm−1K−1, so an unprotected person can succumb to hypothermia even in warmish water on a warm day. Wetsuits are made of closed-cell foam neoprene, a synthetic rubber that contains small bubbles of nitrogen gas when made for use as wetsuit material (neoprene may also be manufactured without foaming for many other applications where insulating qualities are not important). Nitrogen, like most gases, has very low thermal conductivity compared to water or to solids, and the small and enclosed nature of the gas bubbles minimizes heat transport through the gas by convection in the same way that cloth fabrics or feathers insulate by reducing convection of enclosed air spaces. The result is that the gas filled cavities restrict heat transfer to mostly conduction, which is partly through bubbles of entrapped gas, thereby greatly reducing heat transfer from the body (or from the layer of warmed water trapped between the body and the wetsuit) to the colder water surrounding the wetsuit.