The hydrocollator pack is a fabric envelope containing silica gel or bentonite crystals that absorb water and are heated in a hydrocollator unit. The heated packs are wrapped in towels and applied to patients for 30 minutes to provide moist heat therapy. This increases local temperature, circulation, and tissue extensibility while relieving pain and muscle spasms. Proper application and precautions are needed to safely use hydrocollator packs and avoid burns or dehydration.