Heated water in the suit forms an active insulation barrier to heat loss, but the temperature must be regulated within fairly close limits. If the temperature falls below about 32 °C, hypothermia can result, and temperatures above 45 °C can cause burn injury to the diver. The diver may not notice a gradual change in inlet temperature, and in the early stages of hypo- or hyperthermia, may not notice the deteriorating condition. The suit is loose fitting to allow unimpeded water flow. This causes a large transient volume of water (13 to 22 litres) to be held in the suit, which can impede swimming due to the added inertia. When controlled correctly, the hot water suit is safe, comfortable and effective, and allows the diver adequate control of thermal protection, however hot water supply failure can be life-threatening.