Despite being the straight-up lightest bag in our review, the Sea to Summit Spark III was on the warmer side of sleeping bags we tested. In our real-world tests we thought it was a pretty true 25 degree bag.
The chart below shows where the Spark III stands in Overall Performance.
The Spark III is rated as a 25 degree bag. Our testing team felt even despite its impressively low weight, that it was a true 25 degree bag. It features 14 ounces of 850+ fill power down that works to achieve its 25F rating. Check out the chart below to see where the Spark III stands in the Warmth category.
The volume of 850 fill-power down stacks up comparably with other bags, such as the 30 degree Western Mountaineering Megalite
, which features 13 ounces of similar 850+ fill, or the slightly warmer 20-degree Western Mountaineering Ultralite
which features 16 ounces of similar quality/loft down. The Spark III is perfect for cooler weather backpacking trips, where evenings might dip down below freezing, or for folks who sleep a bit on the cooler side.
The Sea to Summit Spark III features a well designed hood that help capture heat along with 14 ounces of 850+ fill power down to achive its 25F rating.
The Sea to Summit Spark III tipped the scales at an impressive 1 lbs 6 ozs the lightest bag in our review. It did this by featuring the lightest shell fabric in our review (10), high quality down, a short 1/3 length zipper (seen all-the-way unzipped here) that was also the smallest-size zipper featured on a sleeping bag in our review.
At one pound six ounces, the Spark III is the lightest bag in our review. Despite being rated to 25F, it remains on the warmer side of all bags we tested; in fact, there are not many bags of comparable warmth that are even close to the weight of the Spark III. The Spark III basically achieves its' best-in-class weight in four ways. The first way the Spark III minimizes its weight is by using a 10D UL Nylon exterior fabric treated with DWR; this makes up the backbone of the bag.
This fabric is the lightest weight nylon used on any sleeping bag we tested. We found this fabric to be totally down proof and durable. It's worth noting that while sleeping bags do not take a ton of external wear and tear, you do need to be careful with sharp objects inside of the tent or with pointy rocks if sleeping out under the stars. The Spark III uses some of the highest quality down, minimizing the amount of extra insulation needed in order to achieve the same warmth. The cut is the tightest among bags we tested, shaving off the few extra ounces that a more spacious bag would contain. Finally, the Spark III features a 1/3 length #3 YKK zipper; both the shortest and smallest sized zipper that we tested.
The Sea to Summit Spark III came with the best compression sack among any sleeping bag we tested.
This contender is the most compact bag in our review. It achieves this via several of the same reasons we just mentioned. This bag is an incredibly low weight option; it's made up of a super light 10D shell fabric, has a 1/3 length smaller than average #3 YKK zipper, is made of high-quality down, and has a tighter cut than many of the other contenders. The Marmot Hydrogen
and Western Mountaineering Megalite pack down nearly as small, but the Spark III still packed down 15-20% smaller. When compared to average 20-30°F bags, the Spark is much smaller, packing down to half the size of the Nemo Salsa 30
or even a third the size compared to The North Face Cat's Meow
or the Kelty Tuck 20
The Sea to Summit Spark III (second from the right) was the most packable sleeping bag we tested. This was even more impressive considering it was warmer than all the other sleeping bag pictured in this photo. From Left-to-Right. The Nemo Salsa, the Sierra Designs Backcountry Bed, the Marmot Helium, the Western Mountaineering Megalite, Sea to Summit Spark III and the Mountain Hardwear Hyperlamina.
Comfort, Spaciousness, and Fit
The Spark III is not spacious; in fact, it was the tightest bag we tested. For those used to classic cut mummy-style bags, the Spark III feels marginally smaller than most; however, for those that struggle with tighter-cut bags, they will find the Sparks 57"/50"/35" dimensions feel like they just got into the bed, and the sheets are WAY too tight. If you want a light bag, but wish it had a little more space, the Marmot Hydrogen
offers slightly more space with 3" more circumference in the shoulders (overall dimensions 60"/56"/39"). While the Hydrogen's dimensions do not appear like they would offer much of a difference, we easily noticed them as soon as we crawled in.
The Western Mountaineering MegaLite
, our Editors' Choice award winner, featured far more room of any contender, with 64"/56"/39" overall dimensions; as a bonus, it's only two ounces heavier. It's worth noting that the Spark III feels a little smaller in the shoulder area than most bags; however, its' leg area is where most folks noticed its smaller diameter cut. The lightweight fabric feels above average against our skin and the Spark III was among the best feeling bags in our review.
Comparing the dimensions of three of the lightest bags in our review; from left-to-right: Sea to Summit Spark III, Marmot Helium, and the widest of the three; the Western Mountaineering MegaLite.
The Spark III is great for trips where weight and packed size are at a premium and is a fantastic option for folks looking for a lightweight bag; however, overall, the Spark III isn't a super versatile option. It's one-third length zipper doesn't allow for a ton of ventilation; this means that using it on warm summer night wont prove to be as pleasant as other options. Despite an overall tighter fit, the shoulder girth is only 1" smaller in diameter than several other non-comfort oriented bags. When using the Spark III, our broad shouldered testers found that they could at least wear a light, or medium weight puffy, allowing the Spark III to be used in cooler temps down to 15-20 F.
The Spark III is a poor option for car camping or shorter trips where you might just be hanging out in the same camp for multiple nights in a row, where weight and packed size are likely to be less of an issue. The Spark III is a rad bag for all weight weenies; it offers enough warmth to make it adequate for light and fast trips, long range backpacking trips, mountaineering and alpine climbing, or even the occasional spring ski mountaineering trip.
The slightly over-thought-out Sea to Summit Spark III storage sack. It has two size/volume options for storing your bag. We'd recommend using the larger of the two, but for road tripping or a cramped apartment the smaller, zipped down option is a nice compromise of maintaining your bags loft while not taking up your whole closet.
Features and Design
This contender doesn't offer a lot of extra
features, with its most appealing aspects being its minimal weight and fantastic packed size (while still offering surprisingly solid warmth). While it features the thinnest shell fabric in our review (10D), it did not "leak" more down than other bags in our tests. In fact, even after a few weeks of use, it leaked less feathery insulation than other bags using thicker nylon shells.
We loved that it came with a proper compression sack that was easily the nicest stuff sack included with any sleeping bag we reviewed. It also fit perfectly into the compression sack, allowing the user to maximize the compressibility of the Spark III without having to throw down another $30 on a lightweight aftermarket compression sack.
Showing the Sea to Summit Spark III's 1/3 length zipper all-the-way open. This partial length zipper was sweet for reducing weight but made it more challenging to regulated temperature on warmer nights.
This bag is best for any trip where weight and packed size are the most important factors. During the testing phase of our sleeping bag review, the Spark became our go-to for summer alpine climbs. We even brought it with us on a mid-spring ski mountaineering traverse in Washington's North Cascades. We think the Spark III would be killer option for any long-distance or thru-hiking adventure. It would also be a great bag for folks who are camping in a colder climate or for those that desire a sleeping bag that offers more warmth.
The Sea to Summit Spark III is on the more expensive side ($440) but if you want a 3-season bag on the warmer-end of things but still want the lightest and most pack-able sleeping bag you can buy then the Spark III is hard to beat.
Value and the Bottom Line
At $469, the Sea to Summit Spark III is one of the most expensive sleeping bags in our review. Despite its steep price, we think it offers several advantages with its' minimal packed volume and exceptionally low weight. In fact, few, if any, options on the market can match it for its weight.