Sea to Summit Spark Sleeping Bag Review

Sea to Summit Spark Review

This post may contain affiliate links, which means I’ll receive a commission if you purchase through my links, at no extra cost to you. Please read full disclosure for more information.

Download the Ultralight Hiking Gear List

Add your name and email to download the Ultralight Hiking Gear List

Invalid email address
We promise not to spam you. You can unsubscribe at any time.

Sharing is caring!

This is a gear review about the Sea to Summit Spark Sleeping Bags in 2024. 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 known as the Spark SPII which I have extensively used and 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 down to a very small pack size. There are so many positives to note about the Spark sleeping bags making them one of the best lightweight sleeping bags for 2024.

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.

Follow along on Social Media

How We Tested

The Sea to Summit Spark Sleeping Bags in this review have been extensively evaluated and researched by the expert author who has more than 30 years of experience in Thru-Hiking, Backpacking, and Hiking. He also spent several years managing a hiking retail store and is regarded as an expert in this field. It was supplied by the manufacturer. They have been rigorously tested by the author in all kinds of weather on multiple backpacking trips. The research, testing, and experience of the author have combined to present this honest and unbiased review. Read the Review Policy for further details.

Sea to Summit Spark Ultralight Sleeping Bag Specifications 2024

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: 5,355 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

Compare Prices:

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: 9,010 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

Compare Prices:

Sea to Summit Spark SP III / 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: 12,920 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

Compare Prices:

Sea to Summit Spark SP IV / 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: 18,615 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

Compare Prices:

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 tossing 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 has 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 2024. 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 a slightly higher fill Hyperdry down. The stated 850+ down is the minimum standard that Sea to Summit has committed to putting 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 in the Sea to Summit Sleeping Bag
850+ Ultra-Dry Down


Let’s take a look at how the sleeping bag is made with features such as the Inner and Outer Shell fabrics, 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 thin it is almost see-through, especially 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 and 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 its water resistance.

Sleeping bag testing the DWR finish and water resistance of the bag
Water-resistant outer fabric is 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, especially good if you are a slide sleeper. The lower region and bottom side of the bag use 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 effect. Washing the bag will fix the clumping issues on a heavily used sleeping bag.

Sleeping bag hood cinched closed
The sleeping bag hood cinched closed

Zips and Draft Tube

The Spark series features either a full zip or 1/2 length zip. The Sp1 and Sp2 feature 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 well-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 at 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 in 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 is 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 has increased in recent years. Although they are a classic mummy style of the 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. Each sleeping bag style from the Sp1 to the Sp4 has been tested to EN standards so you can rest assured that the sleeping bag will keep you warm at the temperatures as reported.

I am normally a cold sleeper unless I eat 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 warm at what temperature.

This is usually the temperature at 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 night’s 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 halfway 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 on 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 within 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 Spark 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 lose a bit of its 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 wash the sleeping bag. 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 – June 2023 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 bag companies that have their sleeping bags independently tested to the EN / ISO standards to ensure the warmth rating is true and not an educated guess like most of the competitors.

Compare Prices:

Sea to Summit Spark Vs The Rest

How does the Sea to Summit Spark compare to other Sleeping Bags in the ultralight class in 2024. Check out my full comparison review of the Sea to Summit Spark and all the Best Ultralight Sleeping Bags 2024.

Best Suited Use

The 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 nighttime 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 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 is one of my all-time favorite sleeping bags in 2024. 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.

Another one of the Best Backpacking Gear Reviews from BikeHikeSafari.

Follow along on Social Media

Frequently Asked Questions

Are Sea to Summit Sleeping Bags any 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.

Does 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.

Sea to Summit Spark Sleeping Bag Review

BikeHikeSafari Gear Review Process

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 and is proudly independent. All reviews on this site are independent and honest gear 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 was a manager of an outdoor retail store and is very experienced in what is important when using and testing gear for reviews like this.

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

Sharing is caring!

Photo of author
About the Author:
Brad is an Australian who has completed the hiking Triple Crown after he hiked the Pacific Crest Trail, Continental Divide Trail and Appalachian Trail. He has hiked on every continent (except Antarctica) and has cycled from Alaska to Ecuador. He is an expert on outdoor gear currently living in Chile.

Download the Ultralight Hiking Gear List

Add your name and email to download the Ultralight Hiking Gear List

Invalid email address
We promise not to spam you. You can unsubscribe at any time.