An electric heating pad for warming a patient. The electric heating pad may be a heated underbody support, heated mattress or heated mattress overlay. An embodiment of the heating pad includes a flexible sheet-like heating element including an upper edge, a lower edge, and at least two side edges. The heating pad may also include a shell covering the heating element and comprising at least two sheets of flexible material (e.g., two sheets may be one sheet folded over to form at least two sheets). The two sheets of flexible material may be coupled together about the edges of the heating element by a weld. The material of the two sheets may include urethane. In some embodiments, a catalyst to accelerate hydrogen peroxide decomposition is coated on or impregnated into an element within the shell, or on the interior surface of the shell.