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Sea to Summit Spark 45 Sleeping Bag Review
The deeper you dive into building the perfect backpacking kit, the more you realize it’s usually better to tailor your gear to the specifics of each trip. While a one-size-fits-all approach works for a lot of gear, the quest for the optimal sleeping bag is where things can get tricky.
Frequently, I’ve been that hiker stuck in a too-warm sleeping bag on a warm Southern California night, sweating it out and cursing my 20-degree bag. Even after converting to more configurable quilts, temperature regulation can be tricky — cue the one-foot-in, one-foot-out dance all night long.
So, I’ve decided it’s time to bite the bullet on a dedicated summer sleep system. I chose to give the ultralight Sea to Summit Spark 45-degree Fahrenheit sleeping bag a try for short trips with certain weather.
The Spark lineup is worth a look for hikers seeking warmer bags as well, as it also includes 30-, 15-, and 0-degree models.
Sea to Summit Spark 45 Sleeping Bag At-a-Glance
Price: $349.00
Weight: 12.8 oz | 363 g
Fill Weight: 5.3 oz.
Compressed Volume: 2.4 L
Compression Sack Weight: 1.3 oz
Lower Temp Rating: 45°F | 7°C
Materials: 850+ fill-power goose down, 10D nylon liner, 10D shell with PFC-free DWR
Who Is This Bag Best For?
The Sea to Summit Spark 45 sleeping bag is designed for ultralight backpackers and adventurers who thrive in warm climates. It’s best suited to summer trips where weather conditions are predictable and overnight lows are mild.
Beyond outdoor adventures, this bag could also be a compact companion for travel — whether it’s for a night in a mountain hut, a hostel, an airport floor, or even to keep in your car for spontaneous overnight stays on a friend’s couch. It’s also light enough to bring on day hikes as an emergency option.
The Spark 45 weighs in at 12.8 ounces, exactly as advertised. With its compression sack, it’s 14.15 oz.
About the Spark
The Spark series is part of Sea to Summit’s broader push to create high-performance, ultralight sleeping systems for a variety of conditions. The 45-degree rating places this bag at the warmer weather end of the spectrum, ideal for summer adventures or trips where weight savings are crucial.
It’s important to realize that in the Spark lineup, the 0 and 15-degree models have features like box baffles and full-length zippers that the warmer 30- and 45-degree models lack. This is because the summer-weight bags are optimized for weight savings. The Spark 45 sticks to a simple sewn-through baffle construction and a shorter zipper to save weight, relying on high-quality down insulation and lightweight materials to do the heavy lifting.
Circumstance of Review
To give the Spark 45 a proper test, I spent a few nights on the Pacific Crest Trail in Angeles National Forest, including a campsite near the top of Mount Baden-Powell. With nighttime temps dipping to the bag’s rated 45 degrees at 9,000 feet, it was the perfect testing ground.
I camped in a Zpacks Duplex tent and stuck to my usual sleep routine — sleeping in my hiking clothes with no extra insulating layers. I’ve also used it on an early August trip in Oregon on the Columbia River Gorge and during a cold night in a campervan.
Sea to Summit Spark 45 Features
850+ Fill-Power Goose Down: The Spark is insulated with RDS-certified, 850+ fill-power goose down. This high-quality down aims to provide warmth while keeping the weight minimal. Despite the bag’s lightness, it maintained a solid level of warmth during my test, even when temperatures approached the bag’s lower limit.
Ultralight, Breathable Materials: The 10D nylon liner and shell fabrics are designed to be lightweight and breathable. While the materials did keep the bag from feeling too sticky or clammy, they still felt durable enough for regular use. The shell has a PFC-free DWR treatment to help with water resistance, particularly around the hood and footbox, which could be useful in slightly damp conditions.
Technical Hood and Ergonomic Mummy Shape: The Spark’s mummy shape is meant to balance warmth retention with comfort, and it does a great job of that without any claustrophobic tightness.
YKK Zipper with Zipper Plow: The YKK #5 zipper, equipped with a zipper plow, is designed to minimize fabric snags. This feature works perfectly, allowing for smooth operation without the annoyance of material getting caught in the zipper track, even with quick adjustments in the dark.
The Zipper Plow ensures the bag’s material never gets caught up in the zipper track.
How It Performed
Heading into my first trip with it, I’ll admit I was a bit skeptical about the Spark’s ability to keep me warm given how light it is. I packed some extra layers and a silk bag liner, just in case. But guess what? They stayed in my pack the entire time.
Even at the coldest point of the night, when the temps hovered around that 45-degree mark, I only felt a slight chill — nothing a quick zip and a tug on the hood cinch couldn’t fix. For a bag this light, I was impressed with how well it performed, especially since I was sleeping in just my sun hoodie and shorts.
The Spark 45 proved to be a solid option for summer backpacking trips where you need to keep your pack light but still want to sleep comfortably, or your favorite sleeping bag or quilt is rated too warm for the weather you’ll encounter.
Sea to Summit Spark 45 Pros
Warmth-to-Weight Ratio and Size: The Spark nails it with an excellent warmth-to-weight ratio, performing well at its lowest limits without supplemental insulation. Fully compressed, the Spark 45 packs roughly the size of a one-liter Nalgene and virtually disappears into your pack.
Comfort: The material is silky smooth, and it didn’t cling or feel clammy or sticky against my skin, even when warm. As someone who can easily get the ick with certain fabric textures, this was one of the better sleeping bag materials I’ve used.
The bag also worked well in different sleep and sitting positions, without any claustrophobia or tightness. Although I’m an inch shorter than the 6-foot-1 height limit for the regular size, it still felt comfortable.
Adjustment strap: The unique off-center hood adjustment strap was a surprising standout feature for me. It’s extremely light, with a soft and spongy feel that reduces the chance of it irritating your face during the night. In past experiences with other bags, I’ve had uncomfortable encounters with scratchy hood straps and plastic adjusters, but this one stayed out of the way and didn’t disrupt my sleep.
Sea to Summit Spark 45 Cons
Compression Sack: The included stuff sack is pretty snug. It can be a bit of a hassle to get the bag packed in. If you prefer a faster camp breakdown or just want to save 1.3 ounces, you might want to leave the compression sack at home.
Versatility vs. Cost: This bag is built for warmer conditions, so its versatility is reserved for only the warmest of trips. At the price point, it may be an expensive choice to justify for hikers recreating in less predictable climates. Spark models rated for colder weather also cost on the higher end compared to comparable products.
Color Options: The Spark’s electric bumblebee aesthetic is the only choice you’ve got, so prepare to embrace the neon yellow vibe.
Overall / Value
The Sea to Summit Spark 45 has earned its place in my regular summer gear rotation, making the prospect of quick and light backpacking trips on warm nights all the more exciting. Though its versatility in backcountry settings is limited to warm nights, the Spark’s compact and lightweight build has me brainstorming other uses, including budget travel and just-in-case scenarios.
The Spark 45 is a traditional mummy bag that somehow weighs less than most similarly rated backpacking quilts. Despite containing less down than some quilts, the Spark performed as promised at its 45-degree rating during testing.
Most other ultralight options in the market are rated around 40 degrees Fahrenheit, making the Spark’s 45-degree rating a unique offering for warm-weather backpackers who don’t need the extra insulation.
At $349, the Spark 45 is not a budget option, coming in around mid-range among its main competitors. However, the 30-, 15-, and 0-degree models are among the most expensive options compared to other brands.
It’s worth mentioning that very few mummy-style bags match the ultralight warmth-to-weight ratio typically seen in quilts the way this one does. This makes the Sea to Summit Spark, across all its temperature ratings, a pioneer in the sleeping bag market and a surprising competitor to ultralight quilts.
Shop the Sea to Summit Spark 45 Down Sleeping Bag
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The Sea to Summit Spark 45 Down sleeping bag was donated for purpose of review
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