Sea to Summit Spark Ultralight Sleeping Bag Deep Dive

Cold-weather camping season has officially arrived in the mountains, and that means it’s time to adjust your sleep system to better adapt to the cooler temperatures. For many, the challenge each year is finding a sleeping bag that packs down small, is lightweight, yet still keeps them toasty warm, and – until now – the perfect combination of these 3 features has been hard to find.

sea to summit spark

Meet the Sea to Summit Spark!

The Sea to Summit Spark 5ºF features a no-frills design that maximizes performance, yet keeps things lightweight with intentional features designed to cut weight. Selling at retail for $589, this bag is top-of-the-line when it comes to warmth, versatility, and weight.

Designed for the gram counters and those who want to minimize the volume of their pack, the Spark 5ºF is a game changer for cold weather camping, and is the ultimate companion for those who want to brave colder temperatures throughout the shoulder seasons and beyond.

See the Sea To Summit Spark Sleeping Bag

sea to summit spark bag

Draft collar along zipper eliminates drafts.

Sea To Summit Spark Specifications

Feature Type Feature Specs What This Means
Weight 2lbs, 2.7oz Incredibly lightweight for a cold weather sleeping bag.
Survival / Lower Limit Rating 5ºF The temperature at which the average person will be able to survive without freezing in this bag.
Comfort Rating 18ºF The temperature at which the average person will be comfortable and warm in this bag.
Gender Unisex This bag is designed to cater to the shapes of both women’s and men’s bodies.
Earth Conscious Uses feather with a Responsible Down Standard (RDS) certification 100% of the down used in Sea to Summit sleeping bags is independently certified to the Responsible Down Standard (RDS), which tracks the down used in this product all the way from the source to the final product to ensure ethical animal treatment throughout the process.
Insulation 850+ Loft Ultra Dry-Down The fill rating is the main factor in a down sleeping bag’s warmth, and 850 is the second highest loft count that Sea to Summit offers. The higher the loft number, the more packable and lightweight the bag will be for the same warmth.
Waterproofing Sea to Summit Ultra Dry-Down Treated with non-PFC Ultra-Dry Down™ treatment to ensure the materials retain their ability to keep you warm, even when wet.
Fit & Shape Broad Mummy Bag Sleeping bag comes with a fitted hood, tapered foot box, and coverage for your whole body while you sleep. Broader shape for more ease of movement.
Fits Up To Height 6ft, 6in The maximum height that of a person that will fit in the “long” version of this bag.
Season Rating 3.5 seasons This bag is great for late fall and early spring camping. However, this bag could be closer to a 4 season bag when paired with a warm sleeping pad and an appropriate sleeping bag liner.
Retail Price $589 Comparable with bags of similar temperature ratings, but exceptionally well made and worth the investment.

See the Sea To Summit Spark Sleeping Bag

Unique Features of The Spark Ultralight Sleeping Bag

Sea to Summit has included a ton of different features to help make the Spark 5ºF compact, insanely lightweight, and an all-around champion when it comes to colder weather campion. Each of these features plays an important role in making this bag a top-of-the-line sleeping bag for year-round ultralight hikers.

sea to summit Spark stats

Broad Mummy Shape

Sea to Summit utilizes its unique “expedition sizing” in the Spark 5ºF to allow for extra wiggle room – even when bundled up. The extra room is designed to allow hikers to increase the bag’s warmth by layering up on jackets and clothes while still having room to move comfortably in your bag. This extra space is enough room to be functional and stay comfortable while not being excessive to maximize weight savings throughout the bag.

Vertical Chest Baffles

The Spark 5ºF also utilizes vertical chest baffles that are designed to keep the down in place. The down in many similar sleeping bags often shifts while you sleep or begins getting clumped together after a season or two of use. The vertical chest baffle design on the Spark 5ºF is key in preventing any dead spots in your bag and ensuring you stay warm throughout your trip.


Sea to Summit made this bag specifically for the gram-counters. The 850+ fill down is incredibly lightweight, and is designed to compress down to a convenient packed size. Meanwhile, the 10D shell and 7D liner also help bring down the weight. The icing on the cake is the lightweight Ultra-Sil compression bag designed for compact storage.

Practical Design

Additional features like Ultra-Dry Down, a draft collar at both the top and along the zipper of the bag, and a contoured foot box make this bag the champion for cold-weather backcountry adventures.

How The Spark Ultralight Sleeping Bag Compares to Similar Bags

It’s easy to see why the Spark 5ºF has such glowing reviews, but how does it stack up to other popular bags on the market? We compared the stats to a few high-rated bags with similar temperature ratings to give you the full picture:

Sea to Summit Spark 5ºF x Mountain Hardwear Bishop Pass 0ºF (Women’s)

While the Bishop Pass may be less expensive than the Spark 5ºF, many features are lost for the reduced cost. The Bishop Pass features a more traditional Mummy shape, and doesn’t offer the Broad Mummy design of the Spark 5ºF.

This means that users will feel more snug and will be unable to toss and turn in the Bishop Pass, even when additional layers of clothes are needed on cold nights. This also makes using a liner more difficult, which means that users are unable to extend the temperature rating of the Bishop Pass. This bag also only features 650+ fill-power, which affects the weight and packable size.

Sea to Summit Spark 5ºF x NEMO Disco 15ºF (Women’s)

The NEMO Disco 15ºF features a broader mummy design – similar to the Spark 5ºF – however, this bag is significantly heavier than the Spark 5ºF and does not pack down to the same small, convenient size in your pack.

The NEMO Disco 15ºF is also only a 3-season bag with 650+ fill power, as compared to the Spark 5ºF’s 3.5 seasons with 850+ fill power. Additionally, the NEMO Disco 15ºF does not feature dry-down. This means that if your bag gets wet, it will lose all warming capabilities which could result in a dangerous situation – especially when camping in cold, snowy conditions.

Sea to Summit Spark 5ºF x Marmot Teton 15ºF (Women’s)

Similar to the Spark 5ºF, Marmot’s Teton 15ºF features hydrophobic down and strategically designed baffles. However, there are a few key differences here that set the Spark 5ºF in a class above. First up is that the Teton 15ºF is heavy – coming in at 3lbs 9.8oz for the “regular” sized version, this bag would be challenging to backpack with, especially for ultralight hikers.

Additionally, the Teton 15ºF only has 650+ fill power, which makes a huge difference in warmth, weight, and packability when compared to the 850+ fill power offered by the Spark 5ºF. Finally, although the Teton 15ºF offers a wider semi-rectangle design, it is still not as versatile for hikers who toss-and-turn in their sleep, or anyone who needs to layer up a bit more on colder nights.

See the Sea To Summit Spark Sleeping Bag

Who is Sea to Summit?

Sea to Summit is known for their innovative, cutting edge gear and the Australian-based brand has stayed a constant leader in the outdoor industry since their founding in 1983. They strive to never make a “me-too” product, and pride themselves in creative solutions that help make your time outside safer and more enjoyable.

This is what Sea to Summit is all about.

See the Spark Ultralight Sleeping Bag, and learn more about Sea to Summit.

Sea to Summit sponsors this post. Affiliate Policy: This article may contain affiliate links, which help fund our website. When you click on the links to purchase the gear we get a commission, and this goes a long way to creating guides, gear reviews, and other excellent content.

Colleen Goldhorn

Colleen Goldhorn is an outdoor industry creative who is based in Montana's beautiful Bitterroot Valley. She has hiked over 1,000 miles of the Appalachian Trail, and continues to be an avid hiker, backpacker, and adventure seeker throughout the Rocky Mountains. Colleen owns a creative studio which specializes in design, photography, and writing for outdoor brands. Her work can be viewed at, or on Instagram.

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