The Sea to Summit Spark range of sleeping bags are ultralight high performance Down sleeping bags perfectly suited to lightweight backpacking, cycle touring and adventure racing. Their low bulk and lightweight materials result in an impressively small pack size so gram counters don't have to compromise on a comfortable nights sleep. The ultralight 10D nylon outer and 10D liner ensure that the down inside the bag lofts fully. The Spark -18C uses box baffle construction to accommodate extra down and reduce cold spots. The Down used in the Spark range is 850+FP responsibly sourced RSD ULTRA-DRY Down treated water repellent down. This protects the down from moisture and ensures a longer lifespan, it down not mean that the Down is waterproof. The Spark -18C features a 3/4 length two way zip for easy access and extra ventilation options. The neck, zipper and hood feature draft collars to prevent your body's hard generated warmth being lost. The Expedition Mummy sizing is a little oversized to allow space for extra layers of clothing or some wriggle room if you're a restless sleeper. Sea to Summit Spark -18C Features 850+ FP Goose Down insulation ULTRA-DRY Down water repellent treatment 10D Nylon shell Mummy fit provides extra space Box-Wall baffles throughout 3/4 side zips Vertical Chest Baffles Sea To Summit Spark -18C Down Sleeping Bag