The Tri-Core Comfort Zone Pillow, featuring Outlast Technology, helps regulate temperatures by absorbing heat when you?re too warm and releasing heat when you?re cold. Outlast was developed by NASA to help protect astronauts from temperature fluctuations, and now youcan use that technology to get a better night?s sleep! In addition to helping regulate your temperature, the Tri-Core Comfort Zone Pillow also helps provide proper alignment of the neck. For back sleeping, a firm cervical roll supports the neck while a shaped center gently cradles the head for better sleep. For side sleeping, the raised side areas help keep the head level for proper alignment of the spine. In order to provide therapeutic benefits and help restore the natural curve of the neck, two very firm cervical rolls provide different support options. Use the larger neck roll for maximum support. Use the smaller neck roll if you are in the adjustment phase or if you prefer slightly less support. For those who are new to sleeping on a cervical support pillow, or prefer gentle support, the ?Gentle? version may be a better option. It may take some time to adjust to this cervical pillow and immediate overuse can actually increase neck pain. Those who slowly ease their way into orthopedic correction, by alternating between this pillow and their current pillow, achieve the best results. The gentle version provides moderate to firm support, while the standard version provides very firm support. The Tri-Core Comfort Zone Pillow is available in two sizes, and conveniently fits into your favorite standard pillowcase. Full Size Pillow: 24" x 16" (61cm x 40.5cm). Mid-Size Pillow: 22" x 15" (56cm x 38cm).