The Sea to Summit Spark I is the lightest and smallest ultralight sleeping bag that we have ever tested, and deserves recognition as our Top Pick for Insane Packability. This hooded mummy bag is a great choice for adventures where literally every ounce counts, and room in the pack is at an absolute premium — as long as it's not very cold out. With the highest EN standard comfort rating in this review, 54F, it is hard to call this a three-season sleeping bag, although one can always wear more clothes to extend the range if needed. While we tested it with success backpacking in the warm desert, it especially inspires us to try it while self supported bike touring or bike packing, when limited space in the panniers means a large stuffed sleeping bag simply won't do. While you may forget that you are carrying this tiny marvel, you surely won't forget how it kept you comfortable at night.
Sea to Summit Spark I ReviewPrice: $300 List | $298.95 at MooseJaw
Compare prices at 3 resellers Pros: Extremely small packed size, super light weight, fully enclosed mummy bag, reasonable price
Cons: Down shifts inside baffles creating dead space, not comfortable below 54F
Bottom line: The lightest and smallest bag in this review is a great summer or emergency bag option.
Manufacturer Stated Temperature Rating: 46F (EN Comfort = 54F)
Measured weight (ounces): 12.7 oz
Manufacturer: Sea to Summit
RELATED REVIEW: The Best Ultralight Sleeping Bags of 2018
Our Analysis and Test Results
While the Sea to Summit Spark I was the sixth highest rated ultralight sleeping bag in our review, placing it squarely in the middle of our rankings, we simply had to give it credit for being perhaps the most unique design that we tested. Before we saw this hooded mummy bag, we thought that 20 ounces was extremely light, but that's nothing compared to this featherweight bag. We are not lying when we say that this bag stuffs down to the size of a softball in its included compression sack, and weighs about as much as one too! As our Top Pick for Insane Packability, this product is literally a game changer, and we can already envision the gears turning inside your head, contemplating what sort of crazy ultralight overnight missions you could pull off with the Spark I tucked into your tiny daypack.
Of course, with such low weight and small size also comes the expected drawbacks. This bag has the highest comfort rating of any bag in our review at 54F, meaning that unless you bring a lot of extra clothes, you are not going to be warm up in the mountains. However, we will acknowledge that as a fully hooded mummy bag, it does wrap one up better than a quilt. We used this bag on nights with a low of 55F, and were surprised that it felt perfectly comfortable at its comfort limit without having to wear extra clothes, something that cannot be said about the other bags in this test.
While the literature that comes with the Spark I says it has a temperature rating of 46F, digging a little deeper reveals that this is an EN standard "lower-limit" rating, and that the comfort rating for this hooded mummy bag is 54F. While it uses 850 fill power ultra-dry treated down, there is only a measly 6 ounces of it filling this entire sleeping bag. No wonder it's so light! As could be expected, the tiny amount of down spread out inside this bag doesn't manage to loft up very much, and we found that the baffles are not filled very full, allowing the down to move around seemingly at will, leaving dead spots without insulation in their wake. At least when you hold this bag, you can't be fooled into thinking it will keep you warm on a cold night — it's readily apparent that it won't.
However, looking at the above chart, you can see that it still ranked higher for warmth than its much higher temperature rated counterpart, the Sea to Summit Ember II. This is because as a hooded mummy bag, the Spark I does a pretty good job of enclosing you within a nice envelope, which isn't the case with some of the poorer performing quilts.
While warmth is clearly its weakest attribute, we were still surprised at how on a 55 degree night in the desert, we slept comfortably inside the Spark I with no extra clothing on. Every other bag we tested required us to have lots of clothing on to use them at their comfort limit, and often we were cold anyway. Paired with some extra clothes and an ultralight Bivy Sack, the range of adventures that could be successfully accomplished with such a light bag certainly grows.
Our Spark I weighed in on our independent scale at 12.7 ounces, slightly heavier than the 12.0 oz. advertised on Sea to Summit's website, but the difference is pretty negligible. The included compression stuff sack weighed an additional 1.2 ounces.
As you can see, it was easily the highest ranked, and was about 2.5 ounces lighter than the next closest sleeping bag, the Western Mountaineering HighLite, which was also a hooded mummy. If the weight alone isn't worth a giant exclamation point, then the size it packs down to surely is! When fully compressed, the Spark I is roughly the size of softball, or perhaps a large orange or small grapefruit. It literally redefines the idea of what size pack you could get away with while backpacking, like perhaps just a running vest?! With such incredibly unique attributes, how could we not award it a Top Pick?
The most important consideration when assessing for comfort is how well a bag fits. We ordered a regular length bag (it also comes in size long), and there is no option for different widths. We found that the bag fit great. It was plenty long enough for our 5'11" tall head tester. We also found that the hood fit over our head comfortably, and there was enough room inside the mummy style bag when completely zipped up to not feel claustrophobic, or to add an extra layer or two.
As you can see, it ranked roughly in the middle of the pack for comfort, garnering the same score as the hoodless mummy Zpacks Classic and the down quilt Katabatic Gear Palisade 30. Our only comfort related complaint was that the draw cord for the face opening, which should tighten up both the neck enclosure and around the top of the hood, dangled in our face and around our neck, as is fairly common amongst mummy bags. The bare-bones design certainly wasn't as refined as our favorite hood and neck draw cord system, found on the Patagonia 850 Down Sleeping Bag 30.
Hooded mummy bags, especially those that only have a half-length zipper, like the one found on the Spark I, are inherently not super versatile. Without the ability to unzip the bag, open it up, or let the feet out, it is very difficult to ventilate on warm nights. However, because it is such a light weight summer bag, some of this problem is alleviated, and we rated it as our most versatile hooded mummy bag.
The high temperature rating means that it is possible to stay fully enclosed in this lightweight bag on a warm summer night and not overheat, something that could not be said for the Patagonia 850 which has a very similar half-zipper hooded design, but are far warmer. The Spark I is still limited by the fact that it can't be used on very cold nights, although we felt that it had enough room to layer up a bit to stretch the range slightly. For those who like the design of the Spark I but simply need more warmth, Sea to Summit also makes a Spark II and Spark III, which have the same design but use more insulation. They are rated to an EN standard lower limit of 35F and 25F respectively (the Spark I has a 46F lower limit rating).
When it comes to features, there isn't much to talk about on the Spark I. As we already mentioned, it has a short left hand side zipper that is only half-length, and there is a draw cord at the side of the collar that tightens up the collar and around the hood. In order to keep the weight down and the design simple, Sea to Summit didn't add anything else.
With very few features, the important thing is that they function well. Despite being short, the zipper is smooth as butter and didn't seem to have the tendency to catch on the fabric, like we found to be happening on the Patagonia 850. The draw cord for the hood and collar works just fine, although there is no padded neck baffle to help block cold air from entering through this face hole. All in all, a simple design fairly well executed.
A savvy owner of the Sea to Summit Spark I could find innumerable instances to use it. Ones that come to our mind are backpacking, fastpacking, bike packing, bike touring, adventure racing, summer time alpine climbing, and traveling. Of course, warm weather water trips are not exempt either, like canoeing, sea kayaking, or even river kayaking or rafting. The only real limitation to this bag is the temperature range where it will be comfortable to use, but if you like the design and want something warmer, there are two more insulated options available as well.
The Spark I retails for $299, which puts it on the lower end of average for this review. While you are certainly not purchasing a whole lot of feathers with that money, you are buying an innovative design that is unlike any other mummy bag we tested. For those who know they can use it, this bag is well worth the money. For those looking for a wider range of use than simply a pure summer bag, we don't think you should spend your money here.
The Sea to Summit Spark I is the lightest and smallest sleeping bag in our review. It is so uniquely small when stuffed into its compression sack that we had to recognize it with our Top Pick award for Insane Packability. Anyone who has an adventure in mind where having the smallest and lightest gear is critical to success should check this bag out.
OutdoorGearLab Member Reviews
Most recent review: July 6, 2017
Have you used this product?
Don't hold back. Share your viewpoint by posting a review with your thoughts...