A hydrocollator is a stainless-steel, thermostatically-controlled tank that heats bentonite-filled hot packs (sometimes called “Hydrocollator packs” or “hot packs”) in water to therapeutic temperatures (typically around 71 °C–74 °C / 160 °F–165 °F).
The packs are then wrapped in towels and applied to the body to relieve pain, relax muscles, improve circulation, and prepare tissues for therapy.