Thermal insulated water pouch inside pillow helps retain heat and provides responsive head and neck support. Thick top layer of hypo-allergenic DuPont® polyester fiber surrounds the pouch and insulator. Patented easy-to-fill pouch Waterbase™ design provides gentle responsive support. Continuously responds to changes in your sleeping position. Select the amount of water to customize the pillow; low amount of water for a soft pillow, moderate amount of water for medium firmness and fill completely for a firm pillow. Clinically shown to improve the quality of sleep and reduce neck pain.