Sea to Summit Spark SPII -2° sleeping bag review: a minimal bag to keep you warm on fast-and-light adventures

Sea to Summit Spark SPII: first impressions

Sea to Summit’s Spark sleeping bags are the lightest and most packable in the brand’s entire range. Designed to deliver versatile warmth on adventures where weight and pack size are at a premium, they feature a stripped-back and minimal design that’s been created to deliver on that brief. The Spark SPII is the second lightest in the line, promising to keep you warm down to temperatures of around 38°F / 4°C.

To maximize weight and packability, Sea to Summit have filled this bag with super-lofty 850+ fill power down. The result is a bag that barely weighs 500g and packs down to the size of a one-liter Nalgene bottle.

To me, this makes it one of the lightest and most packable bags I've ever tested – if not the lightest and most packable bag I’ve ever tested. That status has come at the expense of quite a few sacrifices, however; the Spark SPII offers fewer features than many equivalent bags, while still costing a hefty $409 / £400 when bought directly from Sea to Summit.

Naturally, then, this bag isn’t one for the weekend warriors. It’s for multi-day fast packers and ultralight backpackers for whom grams are more important than pounds (or dollars). Is it worth this initial high investment, then? Or is it too minimal to keep you comfortable outdoors?

Sea to Summit Spark SPII: features

To make the bag so small and light, Sea to Summit have had to make a few sacrifices. Firstly, there’s no neck baffle, which is something I certainly missed on colder nights. Instead, a singular drawcord pulls everything in, which still does a great job of keeping in the heat.

Additionally, Sea to Summit have also done away with an internal storage pocket to bring the weight down further. To be honest, I was happy to see this omitted from this iteration as I never use them anyway, but it might be something worth bearing in mind if you’re a fan of keeping things close to your chest overnight.

Sea to Summit Spark SPII: insulation

In order to make the bag ultra-light and packable, Sea to Summit have used around 300g of 850+ fill power-down insulation in the Spark II. This is the second highest-lofting down used by Sea to Summit, and the result is a bag that’s super lofty, warm and impressively packable – noticeably more so than bags with a similar temperature rating that comprise lesser-quality down. As it’s treated with a PFC-free hydrophobic treatment, the insulation is also more water-resistant and faster drying than untreated down.

To protect that lofty down, the Spark II comes wrapped in a 10D nylon shell. Despite being super soft and comfortable on your skin, I also found that this does a decent job of keeping water out as long as you shake it off quickly and don’t give it a chance to soak in.

Sea to Summit Spark SP II: fit

In a move to further reduce the bag’s pack size and weight, the fit of the Sea to Summit Spark SP II is decidedly tight. To me, I found that this was a trade-off I was always more than happy to make thanks to the bag’s benefits in other departments. But if you like to move around in your sleep, you may find this too restrictive, especially if camping in colder weather and you need to zip it all the way up.

Meet the reviewer

Craig Taylor

Growing up just south of the glorious Brecon Beacons National Park, Craig spent his childhood walking uphill. As he got older, the hills got bigger, and his passion for spending quality time in the great outdoors only grew – falling in love with wild camping, long-distance hiking, bikepacking and fastpacking.

Sea to Summit Spark SP II: in the wild

I first got my hands on this iteration of the Sea to Summit Spark SP II -2° way back in the summer of 2023. As I write this, I’ve used it around a dozen times on trips in various conditions, including two fastpacking trips, a handful of backpacking overnighters, some casual camps in local woodland and an early winter backpacking trip in sub-zero temperatures where I combined it with Sea to Summit’s Ember quilt. Over the last 12 months, it’s become my go-to bag when I need something light and packable for trips with a 25-45 liter pack.

The first thing worth noting about the Sea to Summit Spark SP II -2° is the very thing you’d buy this bag in the first place for: it’s tiny. Seriously, when packed up, it takes up about as much room as a down jacket or a water bottle, and weighs about the same as a loaf of bread. Despite that, it’s still perfectly capable of keeping you warm in some chilly conditions. During my months of testing, I’ve slept in this bag in just my running kit in temps hovering around 41-45°F (5-7°C), and have comfortably spent the night in when layered up in base layers down and a thin down jacket to around 37°F (3°C).

To make it extra versatile, however, the bag also comes with four toggles on the outside that allow you to fasten a quilt, known as Sea to Summit’s QuiltLock system. To test this, I paired the Spark with a -1°C Ember quilt on a chilly winter backpacking trip in Bannau Brycheiniog (the Brecon Beacons) where the temperature outside hit 19°F (-7°C). To my surprise, I stayed toasty warm all night in this combination, convincing me that this might be one of the most versatile four-season sleeping setups out there.

Granted, you’d need to punt for the additional quilt to make this work (which would make it one of the most expensive four-season sleeping setups, too!), but you end up with a versatile system that can keep you comfortable in everything from balmy summer evenings through to freezing winter nights – all for an amazing 900g.

Sea to Summit Spark SP II: the bottom line

Overall, I love the Sea to Summit Spark SP II -2°. To me, it’s the ideal bag for trips when I’m willing to sacrifice bells and whistles in favor of weight and pack size. That being said, it’s still super comfortable and a joy to use, and the added benefit of being able to pair it with a quilt makes it one of the most versatile ultralight sleeping setups for real four-season adventuring. Granted, at $409 / £400, all of that does come at a cost. But if you can afford it, I think the Spark II is hard to beat.

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