The cap opening is large to allow for easy filling of ice cubes or crushed ice. Ideal for application of cold therapy to help reduce pain and swelling from minor scrapes, bruises, muscle aches, sprains and strains. Recommended to help relieve pain, reduce swelling, and speed recovery. Stays cold much longer than gel packs or other cold packs. Suitable for sport injury and first aid. For cold therapy, simply fill the ice bag two third full with ice and water to relieve discomfort from headaches, bruises, migraines, muscle aches and swelling. For heat therapy, add hot water (not boiling, Notice: The temperature for hot water therapy is 50-60?/122?-140?.) to help soothe an upset stomach