Sleeping Bags · #4
Spark 28°F
Sea to Summit
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Ultralight down mummy — a great backpacking bag when every gram counts.
Pros
- Exceptional warmth-to-weight ratio
- Incredibly lightweight and packable
- High-quality 850+ fill-power ULTRA-DRY Down
- Effective at retaining heat for its weight class
- Streamlined design for minimalist adventurers
Cons
- Fabrics are very delicate; requires careful handling
- Snug mummy fit may feel restrictive for some sleepers
- Half-length zipper limits ventilation options
- Higher price point due to premium materials
Best uses
- Ultralight backpacking
- Thru-hiking
- Fast-and-light alpine missions
- Gram-counting adventurers
Specifications
- Temperature Rating
- 28°F / -2°C (EN Limit)
- Fill Power
- 850+ Loft ULTRA-DRY Down
- Shell Fabric
- 10D Nylon
- Lining Fabric
- 7D Nylon
- Zipper
- Half-length YKK #3
- Packed Size (Reg)
- 3.5L
Pricing
Manufacturer list price · checked Jul 14, 2026
Prices move with sales and stock — confirm the live offer at the retailer below.
Full catalog listing & offersBest for
Ultralight backpacking, Thru-hiking, Fast-and-light alpine missions, Gram-counting adventurers
Where to buy the Spark 28°F
Prices and stock change often, so check the current Amazon offer before you buy.
Some links are affiliate links. Buying through them supports our testing at no extra cost to you.
The Sea to Summit Spark 28°F (or Spark II as it's sometimes called) is a serious contender for anyone looking to shave weight off their pack without completely sacrificing comfort. It’s an ultralight down mummy bag designed for fast-and-light missions where every gram genuinely counts. This isn't a bag for car camping or casual overnights; it’s built for backpackers, thru-hikers, and alpinists who understand that less weight translates to more ground covered and less fatigue. What you get here is a streamlined design focused purely on thermal efficiency and minimal bulk. Sea to Summit has put considerable effort into the materials and construction, opting for premium 850+ fill-power goose down, ethically sourced, paired with a lightweight 10D nylon shell and 7D lining. This combination achieves an impressive warmth-to-weight ratio. While the 28°F rating is ambitious for some sleepers, in real-world conditions, it performs admirably down into the low 30s for a warm sleeper, and perhaps a bit higher for those who sleep cold. It’s a specialized piece of gear, and understanding its limitations and strengths is key to appreciating its place in the market.
Who It's Really For
This bag targets the experienced backpacker or thru-hiker who meticulously weighs every item before hitting the trail. If you're counting grams, appreciate minimalist design, and prioritize packability, the Spark 28°F will appeal to you. It's not for those who toss and turn or need ample space inside their bag, nor is it the right choice for someone's first foray into backpacking. It's a high-performance tool for adventurers who know how to manage their layering and sleeping pad choices to maximize a bag's efficiency. You're paying a premium for engineered lightness, and it delivers that in spades for the right user.
Materials and Construction
Sea to Summit doesn't cut corners on materials. The 850+ fill-power goose down is top-tier, providing excellent loft and compressibility. It’s also treated with their ULTRA-DRY Down process, which helps repel moisture and retain loft in damp conditions, a significant advantage over untreated down. The shell and lining are made from extremely lightweight 10D and 7D nylon, respectively. This keeps the weight down but also makes the fabric quite delicate. The half-length zipper is another weight-saving choice, providing just enough access without adding unnecessary bulk or potential cold spots. The differential cut ensures the down can loft fully.
Real-World Performance
In the field, the Spark 28°F lives up to its ultralight promise. It compresses down to an incredibly small size, barely noticeable in a pack. The warmth-to-weight ratio is outstanding; it feels warmer than its stated rating for most average sleepers, especially when paired with a good sleeping pad. The half-zip works well for temperature regulation without adding bulk. However, the snug mummy shape means there's not much room to move around, which can feel restrictive for some. Draft collars and hood cinches are minimal but effective, ensuring heat stays trapped where it belongs.
Weight and Packability
This is where the Spark 28°F truly shines. A regular-sized bag typically hovers around 1 lb 3 oz (540g), which is exceptional for its temperature rating. The packed size is equally impressive, often compressing to about the size of a liter water bottle, or even smaller with a quality compression sack. For backpackers covering long distances, or those with minimalist setups, this weight and packability are a huge advantage, freeing up space and significantly reducing carry weight. It’s a standout feature that justifies the higher price point for many.
Durability and Trade-offs
Durability is the primary trade-off for such extreme lightness. The 10D and 7D fabrics are incredibly thin and require careful handling. You won't want to be dragging this bag across rough ground or sleeping directly on abrasive surfaces. Punctures and tears are a real possibility if you're not mindful. The half-length zipper, while saving weight, limits ventilation compared to a full-length zip. It’s a bag that demands respect and careful use, but for those who treat their gear well, it will hold up. The trade-off is conscious handling for unparalleled lightness.
How we chose
We started with a long list of sleeping bags that people actually buy, cut anything that could not clear our baseline for durability and field performance, then ranked the 10 that were left against the same criteria. Rankings are editorial. No brand pays for placement, and affiliate links never move a pick up or down.
- Load carriage
- How the suspension handles the loads the pack is actually rated for, over long days.
- Real-world durability
- How the material, stitching, or steel holds up after a season of hard use — not how it looks new.
- Performance in bad conditions
- Wind, rain, cold, and grit are the test. Anything that only works on a nice day gets marked down.
- Weight and packability
- Every ounce has to earn its place in the pack, but not at the cost of something that fails in the field.
- Ease of use
- Setup, adjustment, and maintenance with cold hands, in the dark, without the manual.
- Value at its price point
- Compared against the closest competitors in the same tier, not against cheaper gear in a different class.
Spark 28°F — frequently asked questions
- Is the Spark 28°F worth it?
- We rank it #4 in Sleeping Bags. Ultralight down mummy — a great backpacking bag when every gram counts.
- What is the Spark 28°F best for?
- Best for ultralight backpacking, thru-hiking, fast-and-light alpine missions and gram-counting adventurers. Standouts: exceptional warmth-to-weight ratio and incredibly lightweight and packable.
- What are the downsides of the Spark 28°F?
- Fabrics are very delicate; requires careful handling, Snug mummy fit may feel restrictive for some sleepers and Half-length zipper limits ventilation options.
- What are the key specs of the Spark 28°F?
- Temperature Rating: 28°F / -2°C (EN Limit) · Fill Power: 850+ Loft ULTRA-DRY Down · Shell Fabric: 10D Nylon · Lining Fabric: 7D Nylon · Zipper: Half-length YKK #3
- Who It's Really For?
- This bag targets the experienced backpacker or thru-hiker who meticulously weighs every item before hitting the trail. If you're counting grams, appreciate minimalist design, and prioritize packability, the Spark 28°F will appeal to you.
- Materials and Construction — what should I know about the Spark 28°F?
- Sea to Summit doesn't cut corners on materials. The 850+ fill-power goose down is top-tier, providing excellent loft and compressibility.
Compare side by side
Put the Spark 28°F against any other pick on this list — specs, price, pros, cons and reader ratings.