Bottom Line
If you’re an ultralight backpacker looking for one of the lightest and warmest sleeping bags out there, the Sea to Summit Spark 15 is a top contender. Tested in the altitude of the Colorado Rockies during cold nights and in the remote reaches of the Arizona desert in fall, this bag ranks highly on our list of the best backpacking sleeping bags because of its incredible warmth-to-weight ratio and 850 fill goose down. The Spark’s design is a bit wider than competitive bags, making it a stellar solution for side and belly sleepers without sacrificing packability. The 360° down collar and substantial draft tubes are excellent for trapping heat, and the vertical box baffles help maintain warmth by preventing down from shifting – in other words, it’s as comfy and lightweight as sleeping bags get in the backcountry.
However, the Spark’s thin material isn’t as durable as burlier options, and the zipper tends to snag more than we’d like. And, as with most ultralight gear, this bag comes with a considerably higher price tag than much of the competition. But, for folks who want a minimalist sleeping option that prioritizes lightweight functionality and simple comfort over bells and whistles, the Spark 15 may fan the flames of a perfect night’s sleep.
Quick Specs
Sea to Summit Spark 15
Best Ultralight Sleeping Bag
Score: 82/100
Price: $549
Comfort Rating: 29°F
Weight: 1 lb. 9.7 oz. / 2 lb. 0.8 oz.
Fill Power: 850
Fill Weight: 16.9 oz. / 24.2 oz.
Pros
- Ultralight
- Highly packable
- Excellent warmth-to-weight
- Compression sack included
- Draft collar blocks chill well
- RDS certified
Cons
- Expensive
- Thin material
- Zipper can snag
Warmth
Despite its low weight, the Spark is impressively warm – this thing kept us consistently snug from head to toe on frigid evenings between 20 and 25°F. The Spark packs 850 fill power goose down into vertical box baffles, a design that keeps feathers in place and requires minimal redistribution over time. Draft tubes along the zippers and a 360° down collar work together to block out cold air.
That said, the ultralight focus of this model means it’s not as robust against colder conditions as some heavier alternatives. For example, the 15°F bag we tested is comfort rated to only 29°F, and we can confirm: it will feel uncomfortable below freezing. We highly recommend going with the 0°F version if you’ll be camping in temperatures below freezing in the high alpine, open desert, or in shoulder seasons.
Luckily, Sea to Summit offers this bag in several other versions. For the same price, go with the women’s version to get extra down packed through the chest and foot area. Or, choose between 0°, 30°, and 45°F versions – but keep in mind their comfort limits will be around 10-15°F higher than each number. The Spark also comes as a double bag if you don’t mind sharing space, although double bags often feel colder when temperatures dip due to more potential dead space.
Comfort
The Sea to Summit Spark 15 is one of the lightest bags we tested – but you won’t need to sacrifice comfort. Its made from the same soft 10-denier fabric as the liner that feels ultra smooth and soft against the skin. The hood is plenty big enough to accommodate the biggest backpacking pillows.
We also love the roominess of this bag. While it’s still a true mummy shape, the Spark 15 offers more space than competitors through the shoulders and hips to move around – which tummy and side sleepers will love – but still fits snugly enough to minimize cold spots. The vertical box baffles are effective at stopping down from settling or shifting while you roll over in the night, making it a great choice if you’re an active sleeper and change positions frequently. The full-length draft tube blocks out the chill from the zipper, making this bag a cocoon of comfort.
Weight & Packability
The Spark 15 is one of the lightest and most packable sleeping bags out there, so if you’re a long-distance backpacker, ultralight enthusiast, or minimalist, it will check every box for keeping pack weight down. This bag lands in the Goldilocks zone at just 1 pound, 9.7 ounces for the unisex version and 2 pounds, 0.8 ounces for women – it’s plenty warm and easy to carry. The combination of 10-denier material is lighter and easier to pack than many other backpacking bags that use 15D or 20D fabrics, and ultralight down compresses small, perfect for backpackers who want a streamlined backpack with minimal bulk. The included compression sack smashes the bag into a very portable size, although you can save a few more ounces by leaving the sack at home.
Like all ultralight gear, where this bag excels in low weight, it falls a bit short in durability. The emphasis on minimal weight means this bag generally has a shorter life span than bags made with heavier-duty materials. Gear Analyst Ian Krammer learned this the hard way, so you’ll want to keep a close eye out for brambles, sharp rocks, pine needles, and dog claws to avoid potential damage to the interior and exterior. And consider bringing along a patch kit in case your bag snags or tears.
Features
The Sea to Summit Spark 15 is a no-frills bag with a practical feature set. The hood is accommodating and wide to fit the backpacking pillow of your choice and the cinch cords are simple but effective. The zippers are lightweight and durable. But, that’s it as far as features: the Spark 15 stays focused on weight savings. It lacks additional conveniences like a stash pocket, extra zippers, and additional ventilation – which might be a drawback for some. However, we like this pared-down approach: since simplicity keeps weight down, we don’t expect much more from such high-performance gear.
Should You Buy the Sea To Summit Spark 15?
The Sea to Summit Spark 15 is for weight conscious backpackers who count ounces but still want an industry-leading warmth-to-weight ratio. This sleeping bag is incredibly compressible and airy, making it one of our top choices for backpacking trips. Sea To Summit’s efficient vertical box baffles and premium 850 fill goose down is a recipe for saving weight without sacrificing warmth, and the spacious hood and slightly wider design of the bag makes it crazy comfortable for any style of sleeper.
But, the Spark 15 comes up short if you want additional comfort and convenience features. Its minimalist design excludes a stash pocket and extra zippers. The thin material might be a downside for folks who are tough on their gear, need more robust durability, or want a bit of extra insulation in extremely cold conditions. That said, for folks who want a technical 3-season sleeping bag that’s easy to carry and even easier to use, the Spark 15 may be your ticket to a cozy night of rest.
What Other Backpacking Sleeping Bags Should You Consider?
REI Magma 15 Review: Both the REI Magma 15 and the Sea to Summit Spark 15 offer ultralight designs, exceptional warmth-to-weight ratios, and offer top-quality down insulation. But, the Magma 15 is a bit more durable and a lot more affordable, and weighs quite a bit more.
Western Mountaineering Ultralite 20 Review: The UltraLite 20, like the Spark 15, is a performance sleeping bag with similar fill power, minimalist design, and comparable comfort rating. But, this is a great alternative if you’re looking for even higher quality and attention to detail for just a few ounces more.
Zpacks Classic 20 Review: Like the Spark, the ZPacks Classic 20 also emphasizes minimalist design, three-season versatility, and excellent packability. But, the Classic 20 is lighter, costs less, and has a slightly higher fill power.
