A new type of wet physical model that mimics frog body temperature is proposed and tested for performances in the field. The model is made from a piece of sponge made of foam phenol synthetic resin commercially developed for flower arranging. When the water content was maintained between 60 and 70%, the sponge model exhibited a temperature profile very close to that of a real frog (Rana japonica) of comparable size in a range of ambient temperature normally experienced by the frog in the field (15–25 C). Higher water-absorption capability, more ruggedness, and less weight of the sponge model facilitate its use in large numbers in the field than previously proposed models such as those made of agar or plaster, or formalin-fixed frogs.