Vaporization and Production of bubbles. Production of heat and melting are physical changes
Trainers use this substance because the reaction of the product on the skin is an exothermic one. This produces a feeling of warmth and heat. Heating an injury like a sprain with warmth or heat increases blood flow to the area and promotes healing as the flow of blood carries the necessary substances for healing.
Not sure if this is correct but i would choose the steel tray.