The Morrow Project-issued sleeping bag system is a four-piece system consisting of two light-weight mummy-style sleeping bags, a bivouac sack, and a stuff sack for stowage. The two sleeping backs are designed to be used separately, or nested one inside the other to increase insulation and warmth. The system is rated for temperatures as low as -30 degrees Fahrenheit.
d20 Modern Rules: The Morrow Project sleeping bag system provides a +2 equipment bonus on Fortitude saves to resist cold weather. This stacks with the bonus provided by a tent.