Sea to Summit Spark SPIII | Tested and reviewed

The Sea to Summit Spark SPIII offers hikers a remarkable warmth-to-weight ratio and more space compared to many rivals. Its performance and comfort have earned it a Gear of the Year award for 2024 – we take a close look at this impressive 3-season sleeping bag.

from Sea to Summit
RRP  £450.00
Hiker using Sea to Summit Spark SPIII at camp with Gear of the Year award logo

by Ben Weeks |
Updated on

We’ve tested a lot of kit from Aussie brand Sea to Summit over the years, and invariably we’ve been impressed. The Spark SPIII is no exception. It’s an extremely light and packable premium down sleeping bag that offers superb warmth for weight, without the uncompromising fit of most ultralight bags.

It’s stuffed with 850 fill power goose down with a hydrophobic treatment for improved performance in damp conditions (the traditional drawback of down-insulated sleeping bags). There’s plenty of it too, with an impressive 430g fill weight. This gives a comfort rating of -2°C and a lower limit of -8°C. Yet the bag weighs just 665g in total.

Sea to Summit Spark SPIII with zip fully up, half unzipped, and fully unzipped
©Sea to Summit

To achieve this, the shell and lining fabrics are superlight 10D nylon. Box-wall baffle construction throughout maximises down loft and reduces potential cold spots. Yet unlike many highly tapered ultralight bags, which often feel restrictive, the Spark’s added wriggle room makes it pleasantly accommodating. Other features are fairly limited, but you still get a long two-way zip for good ventilation and an easy-cinch hood.

Sea to Summit Spark SPIII zipper
©Sea to Summit

In truth, the Spark SPIII is being retired in 2024, as Sea to Summit launches a fresh suite of sleeping bag models. But it’s still widely available, and remains a very comfortable bag that’s become one of our go-to 3-season sleeping bags for wild camps and multi-day backpacking trips from early spring through to late autumn, and it gets our Gear of the Year 2024 award.

Gear of the year 2024 winner

Hiker using Sea to Summit Spark SPIII at camp with Gear of the Year award logo
Price: £450.00


  • More internal room compared to rivals
  • Super lightweight
  • Excellent warmth-to-weight ratio


  • Lightweight fabrics are a little delicate

Why the Sea to Summit Spark SPIII won Gear of the Year 2024


Hiker sleeping in a Sea to Summit Spark SPIII
©Pete Elliot

What we like most about this bag compared to other lightweight sleeping bags is its superior fit – unlike a lot of tapered mummy styles, which can make you feel like you’re sleeping in a straitjacket, this has a slightly more forgiving cut, resulting in increased comfort. It’s still thermally efficient without being too close or restrictive.

Awesome warmth-to-weight ratio

Internal lining of Sea to Summit Spark SPIII
©Sea to Summit

The use of premium 850 fill power down ensures this delivers superb warmth to weight. That’s vital if you’re aiming to minimise your trail weight on a long-distance walk, or if you just want to pack light for your next wild camp. Yet this is a bag that is still genuinely warm enough for sub-zero conditions.

Compressible and packable

Sea to Summit Spark SPIII in stuff sack next to water bottle for scale
©Sea to Summit

As well as the high-quality down fill, this bag’s superlight performance fabrics mean it compresses very well. Of course, the thin fabrics mean you shouldn’t treat this bag too roughly – not easy when you’re trying to wrestle it back into its minuscule stuffsack. But that does ensure the packed size is impressively tiny for a 3-season bag. Just give it plenty of time to loft before you hit the hay.

How we tested

Our Gear of the Year award winners are, what we consider, the best products in their category that we've tested in the previous 12 months.

The products have all been used in tough real world conditions by members of our rigorous and experienced team.

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