Explanation of how the Eye Warmer’s silicone rubber heating pad functions:
 
The medical-grade silicone rubber is infused with specialised nano carbons that interact with the electric current passing through and produces heat. This design is patented and the materials are appropriately used as a heating pad:- it is flexible, washable, lightweight, low power consumption and can be powered with just a standard 5V USB.
 
More Details:
The thermal energy emitted by the heating pad is within the Far Infrared (FIR) range of 3-12μm wavelength. The human body actually emits Far Infrared range of approximately 4-50μm, hence the rubber heating pad is well within the bounds of own bodies electromagnetic spectrum.