This heavy duty enclosure is filled with a special foam/gel. Just add water to the fill port and place it in your pillow case with the medical-grade cloth face up. The Chillow pulls heat away from your head, quickly dropping the surface temperature. Use the Chillow to help you sleep better during those warm summer months. Not only will you save money by not running the AC as often, but you'll also improve your health. The Chillow can also be used in lieu of an ice pack. Its cooling effect works wonders on sunburns, swollen joints, and strained muscles. In fact, anything you'd use an icepack for, the Chillow can help, without freezing! And because it's not as cold as an icepack, you can use it for a longer period of time without discomfort or melting ice.