From backpacking trips to car camping excursions, the Boost 650 provides the dreamy comfort you need to sleep well outdoors. With an innovative design that allows you to adjust its shape and add warmth when needed, the Boost is one of the most comfortable and versatile sleeping bags ever made. The semi-rectangular shape gives you considerably more internal space than a mummy bag - you'll feel unrestricted and free to sleep in whatever position you want all night long. But more space demands more body heat to warm it up and cold isn't comfortable. That's where WarmZip comes in. Zipping up the WarmZip center zipper transforms the shape of the Boost 650 from a semi-rectangular bag to a thermally efficient mummy bag. It pulls the 650-fill down around your body and reduces the amount of space your body needs to heat. WarmZip gives you the power to add up to 10F/6C to the Boost's temperature rating. Standard Therm-a-Rest features like a puffy draft collar, a draft tube along the entry zipper line and a cinchable hood round out the Boost's bliss-inducing comfort.