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Sea to Summit Spark Sleeping Bag Review [2022] BikeHikeSafari

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This is a gear review about the Sea to Summit Spark Sleeping Bags in 2022. The sleeping bag review covers the whole Sea to Summit Spark Sleeping Bag Range but I have focused on the Sea to Summit Spark 18F also know as the Spark SPII which I have extensively tested.

The Sea to Summit Spark Sleeping Bags all use high quality 850+ hyperdry down, ultralight 10D outer shell fabric coated with a DWR, 7D inner fabric and they pack to very small pack size. There are so many positives to note about the Spark sleeping bags.

There have been a couple of upgrades to this bag in 2019 and again in 2022 that have improved issues with the bag. These improvements have also made the Spark sleeping bags even better.

Keep reading to find out more.

Sea to Summit Spark Sleeping Bag Specifications

Sea to Summit Spark SPI / 40F Specifications

Sea to Summit Spark SPI Sleeping Bag Review

Weight: 12 oz / 340 grams
Down Fill: 6.3 oz / 180 grams
Sleeping Bag Fabric Weight (without down): 5.7 oz / 160 grams
Down fill power: 850+
Hyperdry Down: Yes
Total down loft in cubic inches: 5355 cubic inches of down loft
Zip: Yes, 1/2 length YKK zips
Draft Tube on Zip: Yes
Hood: Yes
Stuff Sack: Yes, a compression stuff sack
Stuff Sack: XXXS
Stuff Sack Compressed Volume: 1.5L

Sea to Summit Spark SPII / 28F Specifications

Sea to Summit Spark SPII Sleeping Bag Review

Weight: 17.3 oz / 490 grams
Down Fill: 10.6 oz / 300 grams
Sleeping Bag Fabric Weight (without down): 6.7 oz / 190 grams
Down fill power: 850+
Hyperdry Down: Yes
Total down loft in cubic inches: 9010 cubic inches of down loft
Zip: Yes, 1/2 length YKK zips
Draft Tube on Zip: Yes
Hood: Yes
Stuff Sack: Yes, a compression stuff sack
Stuff Sack size: XXS
Stuff Sack Compressed Volume: 2.5L

Sea to Summit Spark SPIII / 18F Specification

Sea to Summit Spark SPIII Sleeping Bag Review

Weight: 23.5 oz / 665 grams
Down Fill: 15.2 oz / 430 grams
Sleeping Bag Fabric Weight (without down): 8.3 oz / 235 grams
Down fill power: 850+
Hyperdry Down: Yes
Total down loft in cubic inches: 12920 cubic inches of down loft
Zip: Yes, 1/2 length YKK zips
Draft Tube on Zip: Yes
Hood: Yes
Stuff Sack: Yes, a compression stuff sack
Stuff Sack size: XS
Stuff Sack Compressed Volume: 4.6L

Sea to Summit Spark SPIV / 5F Specification

Sea to Summit Spark SPIV Sleeping Bag Review

Weight: 31 oz / 880 grams
Down Fill: 21.9 oz / 620 grams
Sleeping Bag Fabric Weight (without down): 9.1 oz / 260 grams
Down fill power: 850+
Hyperdry Down: Yes
Total down loft in cubic inches: 18615 cubic inches of down loft
Zip: Yes, full length YKK zips
Draft Tube on Zip: Yes
Hood: Yes
Stuff Sack: Yes, a compression stuff sack
Stuff Sack size: S
Stuff Sack Compressed Volume: 6.6L

Testing the Sea to Summit Spark sleeping bag
During testing the Sea to Summit Spark is quite warm and true to the comfort limit as marked on the bag.

STS Spark Ultralight Sleeping Bags

When Sea to Summit first introduced the ultralight Spark Sleeping Bag range it became a success as they chased the ultralight sleeping bag market. Once upon a time ultralight backpackers and thru hikers were seen as freaks who compromised durability and safety while chasing lower ounces and grams. Now ultralight is mainstream and accessible to all.

Recent upgrades changes to some of the zips on the bags, vertical baffles to prevent down shift while tosing and turning at night and an improved PFC free DWR finish. All of these improvements have increased the ability of the bag to keep you warm at night, increased the functionality of the bags and reduced the environmental impact of the bag.

They have retained the generous internal sizing and commitment to having the temperatures of the bags independently tested to EN standards.

Note: In March 2022 a new sleeping bag standard, ISO 23537, was released as the new sleeping bag standards. Sea to Summit have informed me that they will be testing all their bags to this standard very soon. I like this commitment to ensuring the sleeping bag ratings are independently tested rather than a best guess on how warm you should be like some companies do.

Down type / fill power

The Sea to Summit Spark is filled with 850+ Hyperdry Goose Down in 2022. This is the top of the range down used on any Sea to Summit Sleeping Bag. It is not only lightweight but it also has good water resistance qualities as they use the water repellent hyperdry down.

When you purchase a Sea to Summit Bag you will get a certificate from the International Down Feather Laboratory (IDFL). This certificate will state exactly what Responsibly Sourced Down was used in your Sea to Summit Ember sleeping bag.

When I opened my new sleeping bag I was surprised to learn that my down sleeping bag had slightly higher fill hyperdry down. The stated 850+ down is the minimum standard that Sea to summit have committed to put in your Spark Bag. Sometimes that batch may be a little higher but never lower. Just a small but impressive feature from Sea to Summit

850+ loft ultra dry down
850+ Ultra-Dry Down


Let’s take a look at how the sleeping bag is made with the features such as the Inner and Outer Shell fabics, zippers, baffles, draft tubes, hood and weather resistance.

Outer Shell fabric

The external face fabric of the Sea to Summit Spark sleeping bag is made using a 10 Denier Ripstop Nylon which is coated with a new PFC-free DWR coating to prevent drops of water from entering the bag. The fabric is so light and so thing it is almost see through, specially when you hold it up to the light.

When testing the spark sleeping bag I dropped a significant amount of water on the outer fabric to test the water resistance of the fabric and the water beaded nicely and ran off the fabric. I’m a fan of this ultralight outer fabric and the new DWR coating.

Also good to know if water did somehow enter get into the down the majority of it will not be absorbed thanks to the use of the high quality Hyperdry down.

Inner fabric

The Sea to Summit Spark sleeping bag uses a lighter inner fabric compared to the outer fabric. The 7 Denier fabric is not only ultralight but also resistant to tearing.

I did try to rip the fabric with my hands, Arnold Schwarzenegger style, and it was tough enough not to rip. Or maybe I am just not very strong!

Weather resistance

As mentioned above, I did drop water on the outer face fabric to test the water resistance and quality of the DWR coating. I can confirm it will provide a decent level of water resistance that is at least equal to or better than all the competition in the Ultralight Sleeping Bag market.

The Sea to Summit Spark is good enough to sleep outside under the stars when condensation comes down overnight.

Disclaimer: I do not recommend that you pour a whole bottle of water over your sleeping bag to test it’s water resistance.

Sleeping bag testing the DWR finish and water resistance of the bag
Water resistant outer fabric being tested with a large amount of water during testing.


A couple of years ago the Spark range changed to vertical baffles in the torso area to prevent down shift while sleeping at night, specially good if you are a slide sleeper. The lower region and bottom side of the bag uses a sewn through design to keep weight to a minimum.

The warmer Spark III and Spark IV use full box baffles to fill more down into the bag for greater warmth. Whether you want weight saving or warmth, the baffle design has you covered.

My only critique was the amount of down in each baffle could have been a little higher to prevent down clumping. After a while the down will start to clump a little, this happens to every sleeping bag. Slight overfill will reduce the clumping affect. Washing the bag will fix the clumping issues on a heavily used sleeping bag.

Sleeping bag hood cinched closed
Sleeping bag hood cinched closed

Zips and Draft Tube

The Spark series features either a full zip or 1/2 length zip. With the Sp1 and Sp2 featuring 1/2 length top of the range YKK #3 zips and a draft tube to keep in the warmth. The Sp3 and Sp4 feature full length YKK zips with a zip draft tube.

I tried my best to destroy the zip and tried to snag it on the internal draft collar. All attempts failed. The zip and draft collar are will positioned and prevent snagging. This is an issue on many sleeping bags but not the Spark sleeping bag.

The zip can snag when trying to open the bag. In fact it will snag for most people when they try to open the bag. There is a quirk with almost all YKK zips on sleeping bags. If you try and open them on an angle they will stick. Once you know this, and change how you open the sleeping bag, you will find it works great.

Overall, the zips and draft tubes do a good job and there is not much that can be faulted.

Sea to Summit Spark Zips
Sea to Summit Spark Zips


The hood on the Spark is good and features a full collar the whole way around. There is an oversized drawcord toggle on the right hand side which is a little bigger than it needs to be. The toggle can be cinched tight to close off most of the hood and leave only the nose and mouth in place to get fresh air on those very cold nights.

The neck and hood collars could be a little bigger and could have more overfilled for better heat retention. In my experience the hood collar and neck collar areas of sleeping bags are the first places to get dirty from body oils and sweat which leads to the down becoming more compressed and clumped , making them less efficient at keeping you warm.

When I tested the Sea to Summit Spark I spent a lot of time sleeping on my side and rolling over a lot. The hood did a good job keeping in the warmth.

As mentioned above, maybe a bit more overfill in the hood and draft collars would be a good improvement.

The Sea to Summit Spark Hood and cinch cord.
The Sea to Summit Spark Hood and cinch cord could be a little lighter and smaller diameter.

Stuff Sack

The standard Stuff Sack supplied with the Spark sleeping bag is good and there is no need for anyone to consider upgrading to anything else. It is lightweight and can be compressed with the side straps to compress the bags into a very small size. In fact, the Spark is one of the most compressible sleeping bags in its class of ultralight sleeping bags.


As mentioned above the stuff sac will compress the bag to a smaller size. Refer to the Specification chart for detailed comparisons.


The Sea to Summit Spark series are possibly the most packable of all the sleeping bags in the ultralight class.

Sea to Summit Spark compression stuff sack
Can’t fault the Sea to Summit Spark compression stuff sack


The internal sizing of the Spark sleeping bags have been increased in recent years. Although they are a classic mummy style of sleeping bag, they have been upgraded to expedition sizing which allows most users to be able to wear a down jacket, down pants or down booties inside the sleeping bag with ease.

When testing the bag I wore my expedition weight down jacket inside the bag and I still had plenty of room to toss and turn without feeling constricted. When sleeping on my back or side I found it to be comfortable and able to keep me warm with no issues to report.

A cheap way to turn your bag into a winter sleeping bag is to use another sleeping bag or quilt with any of these bags. The generous sizing will allow you to use one sleeping bag inside another, thus turning your 3 season sleeping bag into a 4 season winter sleeping bag at a much cheaper price.


When testing the bag I found the temperature rating to be true to those stated by Sea to Summit. As each sleeping bag style from the Sp1 to the Sp4 has been tested to EN standards to you can rest assured that the sleeping bag will keep you wamr at the temperatures as reported.

I am normally a cold sleeper unless I ate a very heavy meal before going to bed (which can keep you warmer at night). I am a side sleeper in general and I found the bag to work well when sleeping on my side or back.

It is super important to note that there are 3 temperature ratings listed on each sleeping bag.

Sea to Summit Spark II temperature rating
Spark SpII temperature ratings

Comfort Rating

The Comfort Rating is the most important rating as this is the temperature at which you will be warm and should sleep well. Unfortunately, the sleeping bag industry as a whole fails to use this rating for marketing reasons. But use this as your base for what bag will keep you wamr at what temperature.

This is usually the temperature in which a woman will sleep well without being cold.

Limit Rating

The Limit Rating is used by almost all sleeping bag manufacturers as the temperature rating for the sleeping bag. Few people will get a good nights sleep at the limit rating unless you know your body well enough to know you are a warm sleeper. I know myself well enough to know I am usually half way between the Comfort and Limit Rating for my own personal rating on how warm I will be at night inside a bag.

This is usually the temperature rating that a male, curled up his side, will sleep. Most people will feel cold and not sleep well when sleeping at the limit rating temperatures.

Extreme Limit

The Extreme Limit is the limit which people will not die from hypothermia or extreme cold. You can be guaranteed that if you use the bag at the Extreme Limit you will not sleep at all. If going into the Extreme Limit be sure to get a Thermal Sleeping Bag Liner or even better upgrade to a 4 Season Winter Sleeping Bag.


As mentioned above the sleeping bag is comfortable and designed as an expedition size. This allows you to wear layers of clothing if needed while inside the sleeping bag. Therefore, the Spark Sleeping bags have bigger internal dimensions than most ultralight mummy style sleeping bags.

Caring for your Spark Sleeping Bag

When you have a high quality sleeping bag it is worth taking care to look after it. One of the best things you can do is wear clean backpacking base layers to bed to prevent sweat, dirt and body oil from penetrating the liner of the sleeping bag. You can also use a sleeping bag liner to keep it clean.

How to store your Spark sleeping bag

The Sea to Summit Spark comes with a Lofting bag included with your bag. The lofting bag is not as large as I would like. Many years ago Sea to Summit Sleeping Bags came with a very large cotton lofting bag. I would have liked to see a larger lofting bag at least twice the size of the one supplied.

Like most people I often go weeks and months between hiking trips or bikepacking trips into the backcountry. While not using the sleeping bag I would love to have it stored in a large lofting bag. Maybe that is something that can improve in the future. Having said that, the lofting bag is such a minor complaint that I can overlook this when taking into account the overall quality of the sleeping bag and everything else supplied with the bag.

Sea to Summit lofting bag
Sea to Summit lofting bag could be a little bigger like they used to use years ago.

How to wash your Spark Sleeping Bag

Over time the sleeping bag will loose a bit of it’s loft and you may start to complain that the bag is not as good as it used to be. Maybe it might start to have some funky smells that seem to be a cross between a sweaty gym and an unwashed homeless person. If this occurs it is time to give the sleeping bag a wash. I wrote an article on how to do this so take a look at How to Wash a Down Sleeping Bag, for further details on how to wash your bag.


The Sea to Summit Spark is a premium Sleeping Bag at a premium price. Having said that, they do not cost as much as some of the other premium ultralight sleeping bags on the market at the moment. The Spark Range sits at the higher end of the price range compared to the competitors but that higher price comes with generally better availability.

Edit – May 2022 there are still some supply issues and not all models are available.

No need to join a waitlist or wait for the bags to be made like some ultralight companies. And it is one of the only ultralight sleeping bags companies that have their sleeping bags independently tested to the EN / ISO standards to ensure the warmth rating is true and not and educated guess like most of the competitors.

Sea to Summit Spark Vs The Rest

How does the Sea to Summit Spark compare to other Sleeping Bags in the ultralight class in 2022. Check out my full comparison review of the Sea to Summit Spark and all the Best Ultralight Sleeping Bags 2022.

Best Suited Use

This Spark Sleeping Bags would be perfect for anyone who is sleeping in temperatures above freezing or slightly below in the case of the Spark 4. The following types of trips would be perfect for this bag.

  • Summer hiking in the Rockies or Sierra or North America. Or into the Spring and Fall if using the warmer Spark 3 and Spark 4.
  • Summer hiking in the Alps in Europe or hiking the Camino. The warmer bags will be well suited to 3 season trips in most places.
  • Summer hiking and 3 season hiking in Australia and New Zealand in most areas.
  • Summer trips in South America including Patagonia as long as the night time temperatures are above freezing. You may need the Spark 4 or something with more insulation if heading to the High Andes of Bolivia, Peru and Ecuador.


The Sea to Summit Spark is best suited to anyone wanting a high quality ultralight sleeping bag. The temperature rating for this bag is true to the specification in my opinion and based on my use of the sleeping bag.

If you want a sleeping bag for the summer months and into the shoulder season for warmer climates then this is for you.

When it comes to improvements, I would like to see a lighter weight cinch chord on the hood, overstuffing of down on the hood, collar and neck draft tubes, and a larger lofting bag.

I wonder if they are considering using a higher loft ultrdry down in the future. Some manufacturers are now using 900+ hyperdry and 950+ loft. Once you get that high on the loft rating the down becomes a little more delicate and needs to be looked after well by the user. Just my thoughts.

Overall, the Sea to Summit Spark range of sleeping bags are one of my all time favorite sleeping bags in 2022. There is little to fault, and those faults are so small that it is not enough to make the bag anything less than one of the best on the market.

Are Sea to Summit Sleeping Bags good?

Sea to Summit Sleeping Bags are some of the best quality and lightest weight available. The Spark, Flame, Ember and Alpine Series are particularly good sleeping bags.

Do Sea to Summit Sleeping Bags use Responsibly Sourced Down?

Yes, All the down sleeping bags from Sea to Summit are ethically sourced down that can be traced as responsibly sourced.

How I Review the Gear

The author, Brad McCartney from BikeHikeSafari is a small independent adventurer and outdoor gear tester who owns and runs

BikeHikeSafari is not part of a large blog network like many other outdoor gear review site and all reviews on this site are independent and honest reviews of outdoor products by the author.

The author, Brad McCartney is a very experienced triple crown thru hiker, adventurer and bike tourer having spent 1000s of nights sleeping in a tent and sleeping bag (Read more). He also used to manage an outdoor retail store and is very experienced on what is important when using and testing gear for reviews like this.

BikeHikeSafari will never receive any money for reviews and does not accept sponsored reviews on this website. All the comments in this review are from the author based on his years of experience. Hope this independent review was helpful for you.

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