I recently picked up Sea To Summit's Spark SP1 sleeping bag. The bag was first unveiled at the 2013 Outdoor Retailer Show in August. The Spark SP1 is an ultralight (12.3oz) and incredibly compactable summer sleeping bag (comfort rating of 54°, lower limit of 46°, extreme of 23°) that compresses down to the size of a grapefruit. Literally. It is that small. So small that Sea To Summit had to redesign their compression stuff sack to cinch down that much.
Everything about this bag is beautiful. The white water-resistant shell. The soft, downproof gold lining. The black and gold typography is crisp and contrasts beautifully against the white shell. The bag seems to glow, like a ghost. It perfectly matches Mountain Hardwear's Ghost Whisperer ultralight windbreaker.
The Spark SP1 uses 850+ Goose Down treated with moisture repellent Ultra-Dry Down and has one of the best warmth-to-weight ratios of any sleeping bag available on the market. I was eager to try it out, so to do so I took it out on the Gabrielino Trail, a 28 mile trail that begins at NASA's Jet Propulsion Laboratory in Pasadena and ends at Chantry Flats just east of Altadena. I figured that if I slept below 5,000' temperatures would be manageable for this bag. Knowing that it would be a low of 34° I utilized the Ultralight backpacking technique of sleeping in all of my layers, including a down jacket, socks, gloves, and hat. I wrapped a mylar blanket around my legs before tucking them into the bag.
This adventure was more of an ultralight gear test than a test of the bag's ability to keep me warm, as I knew going in that the night temperatures would be near freezing. That being said, I was amazed at how small this bag compresses to, and even more so how that translates to packing. It literally takes up the same amount of room in my pack as a 1L solo pot. Less bulk means smaller, easier-to-pack pack, which means less weight. All good things. And it's the most beautiful bag I've ever seen.
Once I have a chance to test this bag in warmer weather, I'll create a more in-depth review.