The lightest sleeping bag Sea to Summit has made yet. Pared down to the bare necessities, the SpI is an adventure racer’s dream. Using the warmth of 850+ loft 90/10 Premium goose down, the amazing moisture protection of Ultra-Dry Down, and a micro-weight 10D Nylon shell and 15D lining, Sea to Summit have created one of the best warmth for weight minimalist sleeping bags available. The Spark is an ultra light bag with many possible uses. Its balance of size, weight and warmth make it an excellent summer sleeping bag, especially for weight and space conscious cycle tourers and ultra light walkers. It also works well as a liner bag, slipping inside another sleeping bag to add one or two seasons to its rating. The Spark compresses so small, Sea to Summit had to re-engineer the compression-sacks to make one that reduced sufficiently. The Ultra-Dry Down protection makes the Spark an impressive hard-alpine or adventure racing sleeping bag, where down has never before been a viable option, and weight is simply not tolerated.