Moist Hot Packs Moist hot packs provide superficial heat, transferring energy to the individuals skin by way of conduction. Each subsequent underlying tissue layer is heated through conduction from the overlying tissue, reaching a slightly deeper tissue level than a whirlpool. Like other forms of superficial heating, deeper tissues, including the musculature, are usually not significantly heated. The heat transfer is inhibited by subcutaneous fat, which acts as a thermal insulator, and by the increased blood flow through the area that carries away externally applied heat. Moist hot packs are used most often to reduce pain and superficial muscle spasm, and to improve tissue extensibility. The pack consists of a canvas or nylon case filled with a hydrophilic silicate or other hydrophilic substance, or with sand. The packs are stored in a hot water unit at a temperature ranging from 70degree to 75degree C . When removed from the water, the pack is wrapped in a commercial padded cover, or in six to eight layers of toweling, and placed directly over the injury site for 20 minutes. Commercial hot pack covers may need another layer or two of toweling to ensure ad- equate insulation for the hot pack. The pack should be secured and completely cover the area being treated. As with other forms of heat application, the patient should only feel a mild to moderate sensation of heat. The patient should never lie on top of the pack, as this may accelerate the rate of heat transfer leading to burns on sensitive skin. After 5 minutes of treatment, the area should be checked for any redness or signs of burning. The hot packs also should be checked regularly for leaks, and should be discarded if any leaking occurs. This may become evident when cleaning the unit on a monthly basis. Hydrophilic silicate may accumulate on the bottom of the unit, and should be removed so as not to interfere with the heating element.