The Chiroflow Pillow features a layer of super-soft, hypo-allergenic polyester fiber floating over the top of the water layer base to provide outstanding comfort and responsive support for the head and neck. A thermal insulator fully encases the water layer to prevent body heat from being drawn from the head, neck and shoulders. This is an essential component of the comfort of the pillow. Easy to follow instructions show how much water to add for soft, medium and firm support. Use ordinary tap water. No chemical additives are required.