The Deltaphase® Isothermal Pad is a new approach to body temperature stabilization. It acts as a source of heat, but cannot overheat once it has reached it's phase change . Its constant temperature is based on a thermodynamic principle and needs no electricity or wires, no thermostat or feedback controller. It cannot generate electrical signals or cause interference. It cannot trigger an explosion. It can maintain a small animal at near normal and constant temperature for several hours. The Deltaphase® Isothermal Pad is based on the thermodynamic principle that a heat releasing phase change is isothermal, that is: that it occurs at constant temperature. A unique chemical solution is contained within a durable pouch. At room temperature this solution is in solid form. When heated to 39° the solution becomes fluid. In this state, the pad is activated and ready for use. When an animal (or any cooler object) is placed in contact with the activated pad, heat leaves the solution as it undergoes a phase change back to the solid form. In this phase change, over 30 calories of heat are released per gram of solution, even though the temperature is constant. The pad remains isothermal until all the liquid phase has solidified. Only then does its temperature fall. The transition temperature has been preset to 39° so that a small temperature gradient always exists for heat flow from pad to animal. This heat flow balances heat losses and maintains animal body temperature near 39° for periods up to several hours with 8" x 8" pads. Smaller pads will hold the temperature up to an hour. The smaller pad, the shorter the duration.