Sea to Summit Spark SP2 sleeping bag review – compact and comfortable

The Sea to Summit Spark SP2 is a premium sleeping bag that packs up small for a comfortable and cozy night's sleep out on the trail

Sea to Summit Spark SP2 sleeping bag setup on a beach hero image
(Image: © Graham Cottingham)

BikePerfect Verdict

The Sea to Summit Spark SP2’s impressive warmth-to-weight ratio makes it an excellent sleeping bag for bikepacking, although on balmier double-figure nights it can get a bit hot.


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    Packs down small

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    Impressive levels of warmth for size

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    Fitted shape isn't restrictive and minimizes cold spots


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    Half-zip and fitted shape causes heat build-up on warmer nights

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    Hood is a touch small

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    Premium price

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Investing in your sleeping system is a great way to optimize your bikepacking setup. Not only can you cut a lot of weight and space in your bags which streamlines your packing, but getting a good night's sleep will do wonders for recovery and setting you up for the next day of riding.

Sea to Summit makes some of the best sleeping bags with a broad range of sleeping systems that cover all temperature ranges from hot sticky nights to subzero winter experiences. The Spark SP2 hits a sweet spot for most bikepackers, right in the middle of the range, its compact pack size and lower comfort limit of -2 Celsius means it should be perfect for most summer and shoulder season adventures.

I threw the Sea to Summit Spark SP2 in at the deep end, taking it on a load of bikepacking and camping trips including Rapha’s Pennine Rally, a five-day bikepacking adventure that crosses the no man's land between Scotland and England. So did I sleep well over the trip?

Sea to Summit Spark SP2 sleeping bag setup on a beach

Vertical baffles have extra down and help evenly distribute insulation (Image credit: Graham Cottingham)

Design and specifications

The Sea to Summit Spark SP2 uses a contoured mummy shape with a small hood and a drawstring to cinch the hood shut. A half-zip down the left side has an anti-snag draft excluder to stop heat from escaping, and two sliders in case you need to open the zip from the bottom for extra ventilation. The outer material uses a somewhat fragile feeling 10D Nylon Shell, but I haven’t experienced any issues with durability or wear.

There is 430g of RDS 90/10 premium goose down for insulation with an 850+ Fill Power, which means every ounce (30g) of down will re-expand to over 850 cubic inches after compression for increased warmth and smaller pack size. The down used is Responsible Down Standard (RDS) certified and treated with a non-PFC Ultra-Dry Down treatment and certification is supplied with every bag to prove this. Sea to Summit uses vertical baffles across the torso to hold extra down and stop it from shifting in your sleep while horizontal baffles across the legs help minimize pack size and weight.

Sea to Summit Spark SP2 sleeping bag with the zip indone

The sleeping bag opens up with a half-zip  (Image credit: Graham Cottingham)

The comfort Temp Rating for the Spark SP2 is EN -4 Celsius (38 Fahrenheit), with a lower comfort rating of -2 Celsius (28 Fahrenheit). Not that we would ever want to test it, but the extreme rating (in EN/ISO standard’s words “In this range, a strong sensation of cold has to be expected. There is a risk of health damage by hypothermia) is -18 Celsius (0 Fahrenheit).

Sea to Summit includes a stuff sack with a buckle closure and webbing compression plus a zipped breathable storage bag to maintain its loftyness when you're not adventuring.

Sea to Summit Spark SP2 sleeping bag detail

Just in case you forget the temperature range (Image credit: Graham Cottingham)


I mostly used the Sea to Summit Spark SP2 for summer and shoulder season bikepacking. For single-digit temperatures, the Spark SP2 is spot on and the shape and loft give a very comfortable night's sleep with enough wiggle space without any unpleasant draughts. The comfort levels are narrow though, if temperatures start to rise and you start getting warm, the half zip and narrow shape limits the available airflow for cooling down. On the colder end of the spectrum, taking the Spark down to the lower comfort temperature rating, you can feel the difference between the vertical and horizontal baffles. The added down filling and vertical baffles hold a lot more warmth than the horizontal leg portion, so if you think you are going to be in for a cold night, it's worth packing a warm pair of socks as your legs and feet will get cold first.

I found the hood was a little small which meant my head would often pop out the hood during the night – which was annoying when I wanted to be tucked in. The drawstring is a little fiddly to use but helps keep the hood in place when you really want to keep the heat in. While I would ideally prefer the convenience of a full-length zip, I think the half-zip on the Spark SP2 could be a little longer to make it easier to get in and out with less shuffling.

The Spark SP2 packs down well, and at 538g it’s also reasonably lightweight which is ideal for bikepacking as space is always at a premium. I'm a 'stuff the sleeping bag straight into the drybag/seatpack/handlebar bikepacking bag' sort of bikepacker and I was able to cram the Spark SP2, Sea to Summit Ultralight mat, an Alpkit Kloke bivy, and a few other sleep essentials into a compact 9L handlebar bag. For those that aren’t a direct stuffer, it’s worth noting that it's a little laborious stuffing the Spark 2 into its sack as it's a neat fit. Once in, the clip makes it easy to close the compression straps – although there isn't a lot of space to be gained from post-packing compression as it's already pretty densely stuffed.  

Sea to Summit Spark SP2 sleeping bag zip detail

The zip can open up from the top or bottom, but the half-length limits possible airflow if you start getting too warm (Image credit: Graham Cottingham)


The Sea to Summit Spark SP2  is a super packable sleeping bag that will hit the sweet spot for many bikepackers looking for a compact sleep system for warmth and comfort throughout summer and into the shoulder seasons. Bikepacking kit is always a trade-off between features and portability, and although the narrow shape and half-zip help keep you cozy, they limit airflow, so in warmer weather the Spark SP2 can get a little hot.  

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The lowdown: Sea to Summit Spark SP2 sleeping bag
PerformanceImpressively warm for the pack size, hard to dump heat if it starts getting too warm★★★★
Construction Well made★★★★★
WeightVery light and packable ★★★★
Value for moneyPremium cost but has performance to back it up★★★★

Tech specs: Sea to Summit Spark SP2 sleeping bag

  • Price: $505.00 / £354.98
  • Weight: 538g (actual)
  • Insulation: Down
  • Comfort Limit: -2°C
  • Packed size: 28 x 14 cm 
Graham Cottingham
Senior reviews writer, Bike Perfect

Graham is all about riding bikes off-road, based in Edinburgh he has some of the best mountain biking and gravel riding in the UK on his doorstep. With almost 20 years of riding experience, he has dabbled in downhill, enduro, and gravel racing. Not afraid of a challenge, Graham has embraced bikepacking over the last few years and likes nothing more than strapping some bags to his bike and covering big miles to explore Scotland's wildernesses. When he isn’t shredding the gnar in the Tweed Valley, sleeping in bushes, or tinkering with bikes, he is writing tech reviews for Bike Perfect.

Rides: Cotic SolarisMax, Stooge MK4, 24 Bicycles Le Toy 3, Surly Steamroller

Height: 177cm

Weight: 71kg