What is the fluid?

We use glycerin, FDA approved. This food additive is found in many recipes, the most common being frosting (or icing) on cakes. It is also used in some skin creams, makeup and lipstick. Others use animal-based Glycerin or water combinations.

Will it make my feet hot?

No! It will actually keep your feet cooler in summer and warmer in winter, similar to a car radiator, creating a thermal barrier. Glycerin is a "coolant" also found in some radiator coolants and anti-freeze. Cooling helps reduce inflammation and perspiration.