The Blue Springs series sleeping bags are made with MicroX+ insulation. MicroX+ Insulation consists of multiple denier staple-length fibers that have a siliconized finish for maximum insulation, loft, and compactness. It is an ultra lightweight insulation that has a tremendous weight-to-warmth ratio. The Blue Springs 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. If you choose the 35? option, you will get a second zipper that allows you to zip the bag "half open" on each side, to allow venting or sitting up, which is a neat feature. The Blue Springs is a great backpacking sleeping bag to take along on your hikes that won't take up all the space in your pack or weigh you down. Features: - MicroX+ Double-Layer Offset - Multiple Sizes and Temperatures - 35? Styles Offer a Second Zipper Option - #8 Separating Zippers - Insulated Zipper Baffle - 210T Nylon Ripstop Outer Fabric - 210T Polyester Liner - Compression Stuff Sack Specifications: - Description: Blue Springs +35? - Length: Long - Dimensions: 34" x 86" - Fill Weight: 24 oz. - Total Weight: 3 lb. 0 oz.