The Yellowstone series sleeping bags are made with Techloft insulation. Techloft Insulation consists of multi-hole staple-length micro-denier fibers that have a siliconized finish for maximum insulation, loft, and compactness. The Yellowstone uses a 2-layer offset construction, sometimes called a "bag within a bag." The contoured hood and mummy shape helps seal up your warmth and keep you warmer. The Yellowstone is a great backpacking sleeping bag to take along on your hikes that won't take up all the space in your pack.