Abstract: An apparatus, product formulation, and method for using heat to excite a multi-compound layer to generate infrared wavelength, wherein the apparatus includes 1) a multi-compound TDP layer which can be excited by heat to generate infrared wavelength and 2) a heat-generating chamber separated by a first non-permeable wall, wherein the reservoir and chamber are formed in or supported by a housing. The TDP layer is composed of more than 30 compounds including ZrO, SiO2, SiC2, Al2O3, FeO, MnO2, Cu2O, MgO, ZnO, and Cr2O3. The heat-generating chamber includes a medium for generating controlled heat, preferably a chemical composition made of carbon, iron, water, and/or salt, which is activated upon contact with air (oxygen). The heat can last as long as 16 hours. The function of the heat-generating element is to supply energy to excite TDP multi-compound layer to generate infrared wavelength at 2-18 micrometer (especially at 4-14 micrometer) range, for all types of pain treatment.