The Sea-to-Summit Spark 1 (40-degree) is an ultralight down sleeping bag that weighs 12 ounces (340g) and is insulated with 850-fill power waterproof down. The Spark 1 has a sewn-thru construction and a one-third-length zipper to save weight. When stuffed the Spark 1 packs down to the size of a baseball (1.5L) making it perfect for trips where pack space is at a premium. Its unbelievably low weight will appeal to anyone trying to shave ounces or grams from their pack weight.
Specs at a Glance
- Gender: Unisex
- Weight: 12 oz (Size regular, Length 72″)
- Actual Weight: 12.5 oz on the SectionHiker digital scale
- Fill Weight: 6.3 oz
- Sizes: regular,
- Type: Mummy
- Packed Size: 1.5L
- EN Limit Temperature Rating: 40F (5C)
- EN Comfort Temperature Rating: 48F (8.9C)
- Construction: Sewn-thru
- Girth/Hips/Footbox (size regular): 59″, 51″, 35″
- Insulation: 850 Fill Goose Waterproof Down RDS
- Zipper: One-third zipper, 2-way
- Zipper Side: Left
- Draft Tube: No
- Shell/Liner Fabric: 10D Nylon RipStop with DWR / 7D Nylon RipStop
- Stuff Sack: Compression sack included and a cloth storage bag
- Visit Sea-to-Summit for complete Specs
Ultralight Design Features
At just 12 oz, how did Sea-to-Summit make this sleeping bag so lightweight?
First off, the sleeping bag is quite tapered and is designed to fit you without a lot of extra internal space. I can fit into its 59″ shoulder girth (size regular) but there isn’t a whole lot of extra room for me. The footbox is rather spacious, however, and my feet can easily splay apart comfortably.
Next, Sea-to-Summit uses very lightweight fabrics on the Spark 1 including a silky 7D nylon liner and an ultralight 10D exterior nylon shell. Both of these fabrics are PFC-free.
Finally, the Spark 1’s zipper is only 1/3 length providing extra weight savings. Because it’s a warm-weather bag, it doesn’t have a zipper draft tube or a chest draft tube, which saves additional weight. The zipper is two-way and has a snap at the top so you can unzip and vent the torso if you get too warm. The snap also takes any tension off the zipper, adding to its longevity. However, the zipper does not have any anti-sag taping along its length, again to save weight, so you need to be careful not to have it jam or potentially tear the lining and shell fabric when opening or closing it.
The Spark 1 is insulated with 850 fill power Nikwax “waterproof” goose down which is premium stuff in terms of warmth-to-weight ratio. Higher fill power down like this provides more warmth by weight than lower fill power down and is used to save weight. The waterproofing makes the down dry faster if it gets damp or wet
The down insulation is oriented in vertical baffles over the hips and chest and in horizontal baffles over the legs and feet to help prevent down shift and keep the down where you want it. The baffle construction is sewn-thru, rather than being box-baffled to save weight and keep costs lower. In sewn-thru construction, the top and bottom fabric shells are sewn together to create tubes to hold the down in. While this prevents downshift, it can create cold spots at the seams.
While the Spark 1 is rated for 40 degrees, I’ve found it sleeps a little cold at 50 degrees, even when used with a suitable sleeping pad and long underwear. It’s still a viable option for warmer weather use, but I suggest you shakedown its comfort rating before counting on it close to its comfort limit.
The Spark 1’s mummy hood is pretty standard with a right-side elastic cord that lets you cinch the hood closed. It doesn’t have space for a pillow, but it is wide enough that you can comfortably roll over onto your side while wearing it. The snap at the top of the side zipper helps seal the hood on the left side and maintain its shape even if the side zipper is not fully closed. The hood is also quite unobtrusive if you decide you want to unzip up the sleeping bag and use it more like a quilt.
The Sea-to-Summit Spark 1 (40) is an ultralight sleeping bag that weighs 12 ounces and is optimized for backpacking trips where space and weight are at a premium. It is by far one of the lightest sleeping bags or backpacking quilts available today. For example, a custom Enlightened Equipment Revelation Quilt with comparable specs (fill power, fabric weight) weighs 3 ounces more. The advantage of using a sleeping bag like the Spark 1 over using a backpacking quilt, besides the obvious low weight and packability, is that you’ll have a draft-free experience without needing a bivy sack because it’s completely enclosed. If you prefer a sleeping bag over a quilt and want an ultralight sleeping bag, the Spark 1 is a viable option worth considering.
Disclosure: Sea-to-Summit donated a sleeping bag for review.SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.