There is a lot to like about the Sea to Summit Spark SPII 28—its 850+ fill power goose down, a total weight barely over a pound, and an absolutely miniscule packed volume. There is also plenty to dislike about the Spark II. Our testers particularly detest its narrow dimensions and a zipper that constantly snags. The latter is a huge concern because this zipper is sewn into the bag in a way that doesn't allow you to restart it if the teeth get misaligned. Snag this zipper badly in the backcountry, and you'll be sleeping with an open sleeping bag until you can get it to a tailor to fix. In our view, this durability issue crosses the line between ultralight and ultra-fragile. We, therefore, only recommend the Spark II to those who prioritize weight savings above all else.
Sea to Summit Spark SPII 28 Review
Compare prices at 2 resellers Pros: Ultralight, high-quality goose down, packs down extremely small
Cons: Terrible zipper, uncomfortably narrow, difficult to compress, noisy fabric
Manufacturer: Sea to Summit
Our Verdict
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Our Analysis and Test Results
Performance Comparison
Warmth
The Spark II is stuffed with 12 ounces of 850+ fill power goose down. This is a whole lot of down for a bag that weighs 19 ounces total. The short 1/3-length zipper limits the possibility for heat to escape. Despite these indicators, we weren't particularly impressed with this bag's warmth. It came close to living up to its 28°F temperature rating, but our testers felt warmer in several other comparable bags that chose to include a neck baffle.
Weight
Where the Spark II really shines is in the weight department. At just 1.21 pounds for a size long, it is among the lightest of the 3-season sleeping bags that we've tested. This will surely be appreciated by anyone in the ultralight crowd that prefers a full mummy hood. Considering its respectable warmth, this also means that the Spark II has an awesome warmth-to-weight ratio.
Comfort
In any sleeping bag design, there will inevitably a balance of trade-offs. And with this bag, the Sea to Summit product designers seem to have traded away comfort. Our testers found its meager interior dimensions to be uncomfortably constrictive, particularly for the lower legs and feet. The fabric also has an unusual coating that makes it noisier than most bags we've tried. If comfort or roominess is paramount, we suggest selecting something with a few more inches in girth.
Packed Size
We were able to compress this bag down as small as any backpacking sleeping bag we tried. We learned this using the same third-party compression sack that we used in all our tests, but the Spark II comes with its own lightweight sack that's capable of full compression. We disliked this sack, however, because it is sized so small that it is difficult to cram the sleeping bag all the way inside. This difficulty is worsened because the shell fabric 's seems to trap air inside in a way that other bags didn't. Our testers were routinely frustrated, waiting for air to escape so that they could finally close this undersized sack.
Versatility
If you hope to use the Spark II across a wide range of temperatures, then you should also plan to be uncomfortable. Its 1/3-length zipper hardly provides the means to vent excess heat on warm nights. At the same time, the lack of a draft collar ensures that precious heat will escape out the hood during cold conditions. Combine these two issues and prepare to sweat or shiver if overnight lows are anywhere outside the narrow range of 40 to 55°F.
Features and Design
Here at OutdoorGearLab, we are usually in full support of ultralight designs, but in the case of the Spark II it seems that just too much has been sacrificed for the sake of trimming ounces. We particularly dislike the small zipper (YKK #3) that was constantly snagging. The end of this zipper is inexplicably sewn directly into the bag, which means that if it snags badly, there is no way to back it down and get it restarted.
For an expensive sleeping bag, the Spark II also comes with a seemingly cheap drawstring. This drawstring, along with the zipper pull tab, is scratchy and prone to rubbing your face in a way that disturbed the sleep of several testers.
Value
To get your hands on this ultralight bag, you have to lay down a hefty pile of money. This is understandable considering the premium 850+ fill power down it contains. The overall performance of the bag, however, does not live up to this price tag in our opinion. For this reason, we don't believe it's an especially good value.
Conclusion
It can be tempting to select a sleeping bag based on the numbers. The Spark II is warm down to 28°F and weighs just 18 ounces, where do I get one?!? In the performance areas that are harder to measure, however, such as comfort, versatility, and design, this bag simply doesn't excel. For this reason, we suggest weight-conscious shoppers consider some of the other backpacking sleeping bags that are still lightweight but don't sacrificing performance in other areas.
— Jack Cramer