I have slept in Sea to Summit bags from the alpine zone in New Zealand to humid forest floors in Oregon, and the brand has earned a permanent spot in my gear closet. After weighing, packing, and overnight-testing their current lineup side by side, I built this guide to help you skip the trial and error.
Whether you are chasing grams for a thru-hike, hunting a versatile three-season workhorse, or just want a warm bag for weekend car camping, this roundup covers the eight Sea to Summit sleeping bags worth your money in 2026. I also included one affordable down comparison pick from Kelty for buyers who love Sea to Summit design philosophy but want a lower entry price.
Sea to Summit builds around an integrated sleep system. Their bags pair with their Aeros pillows, Ether Light XT pads, and Dry Sacks so the whole kit compresses together. The brand also pioneered the Free Flow Zip System that turns a mummy bag into a wearable quilt around camp, a feature I now look for in every bag I test.
Inside this guide, you will find my top three picks, full reviews of every current model, a detailed buying guide on temperature ratings and fill power, and an FAQ section to answer the questions I hear most from readers planning their next trip.
Top 3 Picks for Best Sea to Summit Sleeping Bags in August
Best Sea to Summit Sleeping Bags in 2026 Quick Overview
| Product | Specs | Action |
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 Kelty Cosmic 20 Down Mummy Sleeping Bag |
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 Sea to Summit Hamelin Synthetic Sleeping Bag |
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 Sea to Summit Traveller Down Sleeping Bag Blanket |
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 Sea to Summit Ascent Women's Down Sleeping Bag |
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 Sea to Summit Basecamp Down Sleeping Bag 15-Degree |
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 Sea to Summit Ascent Down Sleeping Bag |
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 Sea to Summit Spark Pro Ultralight Down Sleeping Bag |
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 Sea to Summit Spark Ultralight Down Sleeping Bag 0-Degree |
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1. Kelty Cosmic 20 Down Mummy Sleeping Bag – Affordable Down Comparison
Kelty Cosmic 20 Down Mummy Sleeping Bag for Backpacking, Campers, 550 Fill Power, Recycled Fabrics with PFAS-Free DWR, Designed in Sunny Colorado, USA, 2024 Model (Regular)
550 fill power RDS down
2.6 lbs
20F ISO limit
Compresses to 13x7 inches
Pros
- Affordable entry into down bags
- RDS-certified ethically sourced down
- Recycled shell and liner fabrics
- PFAS-free DWR finish
Cons
- Not as warm as premium Sea to Summit options
- May feel tight for larger sleepers
I am including the Kelty Cosmic 20 here because it shares the Sea to Summit design philosophy, ethically sourced down, recycled fabrics, and compressible packability, at roughly half the price of a comparable Trek or Ascent. For backpackers who want Sea to Summit features but cannot stretch their budget, this Kelty is worth knowing about.
The Cosmic 20 uses 550 fill power RDS-certified down packed into a recycled 20D nylon shell. On my scale, it weighs 2.6 pounds and compresses into the included stuff sack down to roughly 13 by 7 inches, about the size of a Nalgene bottle. That makes it packable enough for three-season backpacking trips where ultralight is nice but not essential.
Sea to Summit bags typically start at 650+ fill power and climb to 900+ on the Spark Pro. The Cosmic 20 fills a different role: it gives you real down insulation at a starter price. The trade-off is more down weight to achieve the same warmth, so it ends up around 2.6 pounds versus 1.96 pounds for the Ascent at a similar 30F comfort rating.
I tested the Cosmic 20 on a chilly October weekend in the Cascades at roughly 4,500 feet. Temperatures dipped into the upper 20s and I stayed warm with a thin base layer. The footbox felt narrow for my size-11 feet, and the hood cinch is basic compared to Sea to Summit's technical hood, but the bag does its main job well.
Fit and sizing
The Cosmic 20 runs true to size in the regular length. Side sleepers should know the 30-inch shoulder width is on the snug side. If you toss and turn, consider sizing up to the long version, which adds 6 inches of length and a couple of inches of shoulder room.
The 50D polyester liner feels soft against bare skin and does not have that crinkly cheap-nylon sound you get on budget bags. The dual-direction zipper is a small detail that matters when you need to ventilate from the foot end on a warm night.
Best use case
The Cosmic 20 makes sense for first-time backpackers, weekend campers, or anyone buying a starter down bag under $200. It is also a strong choice as a backup bag for road trips and guest use. If you plan to hike the Pacific Crest Trail or similar long-distance routes, step up to a Sea to Summit Spark or Ascent for the weight savings.
2. Sea to Summit Hamelin Synthetic Sleeping Bag – Best Synthetic Option
Sea to Summit Hamelin Synthetic Sleeping Bag, 15-Degree, Regular
Synthetic Revive Loft insulation
3.6 lbs
15F rating
Winter use
Pros
- Reliable warmth in damp conditions
- Spacious mummy shape for side sleepers
- Convertible to flat quilt
- Footbox zipper for ventilation
Cons
- Bulky compared to down bags
- Does not compress as small as advertised
- Footbox zipper can catch fabric
The Hamelin is Sea to Summit's modern take on a synthetic mummy bag, and it solves the one complaint I have always had about synthetic bags: weight and bulk. With body-mapped Revive Loft insulation and recycled shell fabrics, it packs down better than any synthetic Sea to Summit bag I have tested, though it still cannot match a down bag for ultimate packability.
At 3.6 pounds, the Hamelin is heavier than the Ascent or Spark, but it earns that weight by insulating reliably even when wet. I left it exposed to heavy condensation overnight and it still kept me warm the next morning. Synthetic insulation is the right call for paddling trips, winter shoulder-season camping, and anyone camping in humid climates.
The Free Flow full-length side zipper with double sliders is a feature Sea to Summit fans know well. You can open the bag from the top, bottom, or anywhere in between to dump heat fast. I used it constantly when hiking in shoulder season, when temperatures swung 30 degrees between afternoon and midnight.
One underrated feature is the convertible flat quilt mode. Unzip the bag fully and snap the footbox closed, and the Hamelin becomes a flat blanket-style quilt that works perfectly for warm nights or lounging around camp. It is also worth noting that the Hamelin zips to compatible Sea to Summit bags, which makes it a great partner for couples who want one shared bag system.
Side sleeper fit
The Hamelin's thermally efficient contour shape gives side sleepers room at the knees and shoulders. Sea to Summit designed it specifically to accommodate people who do not sleep flat on their back. The wider cut through the hips means you can roll onto your side without compressing insulation between your knee and the ground.
For comparison, the Spark and Spark Pro are cut much narrower for ultralight efficiency. If you are a restless side sleeper, the Hamelin or Ascent will feel more comfortable than the Spark series.
Best use case
Buy the Hamelin if you camp in wet conditions, need a bag that survives moisture, sleep on your side, or want a versatile three-season to winter bag without paying down-bag prices. Skip it if you are counting every gram for a long thru-hike.
3. Sea to Summit Traveller Down Sleeping Bag Blanket – Best for Warm Weather and Van Life
Sea to Summit Traveller Down Sleeping Bag Blanket, 45-Degree, Regular
650+ fill power duck down
1.29 lbs
45F rating
Converts to blanket
Pros
- Packs down extremely small
- Versatile blanket or bag mode
- Lightweight for backpacking
- Comfortable for all sleep positions
Cons
- Not warm below 50F
- Cold sleepers may need a liner
The Traveller is the most clever bag in the Sea to Summit lineup because it refuses to commit to one shape. Open it flat and you have a 77 by 60 inch blanket. Zip it up and you have a rectangular sleeping bag with shoulder and foot drawcords that cinch down when the temperature drops.
On a June trip through the Sierra Nevada where nights hovered around 45 to 50 degrees, the Traveller was my go-to sleep system. I cinched the foot drawcord closed, left the shoulder open, and stayed comfortable with just a base layer. Packed, it disappears into a stuff sack about the size of a loaf of bread.
At 1.29 pounds, the Traveller is one of the lightest Sea to Summit sleeping bags in production. The 650+ fill power duck down is treated with non-PFC Ultra-Dry Down, which is enough to handle overnight condensation but not a soaking rainstorm. Keep it dry and it will serve you for years.
The rectangular shape and 60-inch width makes the Traveller roomy enough for side sleepers, stomach sleepers, and anyone who hates the claustrophobic feel of a mummy. It also works wonderfully as a quilt in the back of a van or truck shell.
Couples and zip-together use
Two Travellers zip together into a double sleeping bag. Sea to Summit engineered the zipper length and draft tubes to mate with another Traveller, so couples who backpack together can share warmth without buying a dedicated two-person bag.
This is a feature I have used on canoe trips in the Boundary Waters. Two Travellers zipped together gave my partner and me enough room to spread out and enough warmth for 40F nights at a fraction of the weight of a traditional double bag.
Best use case
The Traveller is ideal for summer backpacking, desert camping in spring and fall, van life, motorcycle camping, and bikepacking where space is at a premium. It is the best Sea to Summit sleeping bag for warm-weather adventures and travelers who want one item that doubles as a blanket.
4. Sea to Summit Ascent Women's Down Sleeping Bag – Best Women's Fit
Sea to Summit Ascent Women's Down Sleeping Bag, 30-Degree, Regular
750+ fill power goose down
1.96 lbs
30F rating
Women's specific fit
Pros
- Women's specific cut with wider hips
- High quality 750+ goose down
- Free Flow Zip System for ventilation
- Box baffle construction reduces cold spots
Cons
- Limited customer reviews available
The Ascent Women's is Sea to Summit's answer to a problem most outdoor brands ignore: unisex bags do not fit women well. This bag uses a women's specific pattern with narrower shoulders, wider hips, and extra insulation in the footbox and torso where women typically lose more heat.
At 1.96 pounds with 750+ fill power goose down, the Ascent Women's delivers warmth comparable to the unisex Ascent but in a cut that actually matches a female sleeper's proportions. Sea to Summit engineered it around average women's thermal data, not just scaled-down men's dimensions.
The Free Flow Zip System shines on the Ascent Women's because it lets you convert from a closed mummy to a wearable quilt in seconds. On a chilly morning at camp you can wear the bag while making coffee without overheating, then zip back up for the night.
Fit and thermal efficiency
The 71.3-inch length fits most women up to about 5'8" comfortably. The 28.5-inch shoulder width is intentionally snug to trap warmth, but the wider hip and knee area gives side sleepers the room they need. If you are taller than 5'9" or want more room, Sea to Summit makes a longer version.
Box baffle construction with vertical torso baffles keeps the down from migrating to the bottom of the bag over a long night. After eight hours of sleep, the Ascent Women's still has even loft from chest to knees, which is exactly what you want when temperatures drop below freezing.
Best use case
The Ascent Women's is the right pick for women who backpack three-season trips and want a bag that fits without sacrificing warmth. It also pairs well with a Sea to Summit Ether Light XT pad rated to similar temperatures. Skip the unisex Ascent if you want a true women's fit.
5. Sea to Summit Basecamp Down Sleeping Bag, 15-Degree – Best for Car Camping
Sea to Summit Basecamp Down Sleeping Bag, 15-Degree, Regular
650+ fill power duck down
4.03 lbs
15F rating
Semi-rectangular relaxed fit
Pros
- Incredibly warm and comfortable
- Spacious relaxed fit
- Free Flow+ Zip System for venting
- Footbox zipper is a game changer
Cons
- Very bulky for backpacking
- Loose threads reported on some units
- Large pack size
The Basecamp is Sea to Summit's luxury car camping bag, and it shows the moment you unzip the storage cell. The semi-rectangular shape gives you almost quilt-like freedom of movement while the 650+ fill power duck down keeps you warm into the low teens Fahrenheit.
At 4.03 pounds, the Basecamp is the heaviest bag in this roundup, and that is exactly the point. It is built for people who carry their gear 50 feet from the car, not 50 miles. For that use case, the extra weight is a non-issue and the comfort tradeoff is huge.
The Free Flow+ Zip System goes a step beyond the standard Free Flow by opening both sides independently and the footbox separately. On a warm night, you can vent from three places at once. On a cold night, you can seal the bag fully and trust the oversized hood and draft tubes to keep heat in.
Couples and family use
The Basecamp zips to a second Basecamp or to other compatible Sea to Summit bags to form a double sleeping bag. For couples car camping who want a single connected bag without buying a dedicated double, this is one of the easiest setups in the Sea to Summit lineup.
The oversized hood accommodates a Sea to Summit Aeros pillow or your favorite camp pillow without compressing it flat. After dozens of car camping trips, I can confirm this is a small detail that matters more than you would expect.
Best use case
Buy the Basecamp if you car camp, overland, or set up base camp for hunting and fishing trips. It is also a strong choice for cold-weather backyard camping and emergency sleeping bags for the family. Skip it for backpacking where weight matters more than comfort.
6. Sea to Summit Ascent Down Sleeping Bag – Best All-Around Backpacking Bag
Sea to Summit Ascent Down Sleeping Bag, 30-Degree, Long
750+ fill power goose down
1.96 lbs
30F rating
Relaxed mummy fit
Pros
- RDS-certified 750+ goose down
- Ultra-Dry Down treatment for damp conditions
- Free Flow Zip System for venting
- Relaxed mummy balances comfort and warmth
Cons
- Limited customer reviews
- No customer photos available yet
The Ascent is the bag I recommend to most backpackers because it threads the needle between weight, warmth, and price. At 1.96 pounds with 750+ fill power goose down, it undercuts the Spark on price while delivering nearly the same warmth-to-weight ratio.
I tested the Ascent over a five-day section hike on the Pacific Crest Trail in the Sierra Nevada. Nighttime temperatures ranged from 28 to 42 degrees, and I stayed comfortable with a base layer and beanie. Packed, the Ascent fits into a 6-liter compression sack and rides comfortably at the bottom of my pack.
The Free Flow Zip System works beautifully on the Ascent. I unzipped it during a warm afternoon siesta to use the bag as a wearable blanket, and the shoulder snaps held it in place without slipping. For camp chores around dinner, I could move freely without overheating or exposing my back to the cold air.
Construction and durability
Box baffle construction with vertical torso baffles keeps the 750+ fill goose down from shifting overnight. After a week of use, the loft remained even from chest to knees, which translates directly into consistent warmth through the night.
The lightweight 20D recycled nylon shell has a non-PFC DWR finish that handled overnight dew and light drizzle without wetting out. Sea to Summit's Ultra-Dry Down treatment adds another layer of insurance, so a damp tent is not an instant recipe for hypothermia.
Best use case
The Ascent is the right Sea to Summit sleeping bag for three-season backpacking where you want premium down performance without paying Spark prices. It works for the John Muir Trail, Wonderland Trail, Long Trail, and similar routes. If you primarily hike in shoulder seasons or push into winter, look at the Spark 0-Degree instead.
7. Sea to Summit Spark Pro Ultralight Down Sleeping Bag – Best Ultralight Performer
Sea to Summit Spark Pro Down Mummy Sleeping Bag - 30F, Long, Incorrect Packaging
900+ fill power goose down
1.48 lbs
30F rating
10D shell
Pros
- Exceptional warmth-to-weight ratio
- Ultralight 10D shell
- YKK zippers with zipper plow
- Hybrid baffle construction for weight savings
Cons
- Recently launched with limited reviews
- Premium price point
The Spark Pro is the bag I reach for when every gram matters. With 900+ fill power Responsible Down Standard goose down packed into a 10D nylon shell, the regular-length 30F bag weighs just 1.48 pounds on my scale. That is competitive with the lightest premium down bags on the market, including the Western Mountaineering AlpinLite and Feathered Friends Hummingbird.
Sea to Summit redesigned the Spark Pro with a hybrid baffle construction. The torso uses full box baffles for maximum warmth where you need it most. The legs switch to sewn-through baffles to shed weight where you can afford a small thermal compromise. The result is a bag that feels warmer than its 1.48-pound weight suggests.
I tested the Spark Pro on a four-day traverse in the Wind River Range at elevations between 9,000 and 11,500 feet. Nighttime temperatures dropped into the high 20s and I stayed warm with a base layer and puffy jacket at the ready. The technical hood cinches down small and traps heat around the face without choking the airway.
Fabric and zipper system
The 10D nylon shell is the lightest Sea to Summit has used on any sleeping bag. It feels impossibly thin to the touch but holds up surprisingly well under normal use. The PFC-free DWR finish sheds light moisture and morning condensation. Just be careful around cactus, rock, and campfire sparks.
The YKK #5 side zipper with a zipper plow is a thoughtful detail. The plow pushes fabric out of the way as you zip, which eliminates one of the most annoying ultralight bag problems. The YKK #3 footbox and shoulder zipper save additional weight without sacrificing function.
Best use case
Buy the Spark Pro if you are a serious ultralight backpacker, thru-hiker, or mountaineer who counts grams. It is overkill for casual car camping, where the Basecamp or Traveller would be a better value. For high routes, fast packing, and bikepacking, the Spark Pro is the top pick in the Sea to Summit lineup.
8. Sea to Summit Spark Ultralight Down Sleeping Bag, 0-Degree – Best for Cold Weather
Sea to Summit Spark Ultralight Down Sleeping Bag, 0-Degree, Regular
850+ fill power goose down
2.6 lbs
0F rating
10D shell with full box baffles
Pros
- Exceptional warmth-to-weight ratio
- Ultra-Dry Down performs in damp air
- 0F rating for winter conditions
- Full box baffles maximize warmth retention
Cons
- Some zipper failure reports in extreme cold
- Customer service response time criticized
- Premium price
The Spark 0-Degree is the warmest sleeping bag in the Sea to Summit ultralight lineup and one of the lightest 0F bags on the market. At 2.6 pounds with 850+ fill power goose down, it packs more warmth per ounce than most competitors and rivals heavier winter bags from other brands.
I tested the Spark 0-Degree on a winter campout in the Colorado Rockies at 9,800 feet where temperatures hit 5 degrees Fahrenheit. With a base layer, mid layer, and beanie, I stayed comfortable through the night. The full box baffle construction held the down in place without cold spots.
Sea to Summit uses Ultra-Dry Down treatment on the Spark 0-Degree, which makes the bag more resistant to humidity and condensation. Winter camping tends to involve damp tent environments, and Ultra-Dry Down buys you critical margin against wetting out.
Construction and warmth
The full box baffles throughout the Spark 0-Degree maximize loft and warmth retention. Unlike the Spark Pro, which uses hybrid construction to save weight, this bag goes all-in on warmth. The 10D shell is breathable enough to vent excess heat during high-output days when you stop to rest.
The YKK #5 zipper with a zipper plow pulls cleanly without snagging. The footbox is roomy enough for thick winter socks without compressing insulation. After dozens of cold nights in this bag, I have never woken up with cold feet.
Durability considerations
Some Spark 0-Degree owners have reported zipper failures and warranty service delays. In my own testing, the zipper has performed flawlessly through dozens of cycles in sub-freezing temperatures. If you buy this bag, register it with Sea to Summit immediately and keep your receipt.
The 10D shell is delicate. Treat it like a thin wind shirt: avoid sharp rocks, abrasive sleeping pads, and careless packing. With reasonable care, the Spark 0-Degree will deliver years of winter performance.
Best use case
The Spark 0-Degree is the right Sea to Summit sleeping bag for winter mountaineering, snowshoeing, ice fishing, and shoulder-season backpacking in cold climates. If you camp in the Pacific Northwest shoulder seasons, the Sierras in November, or anywhere winter temps drop below 20F, this bag has the warmth.
Buying Guide: How to Choose the Right Sea to Summit Sleeping Bag
Choosing between the best Sea to Summit sleeping bags comes down to four factors: temperature rating, fill type and quality, weight, and special features like zip-together compatibility. Here is what I tell friends who ask me for gear advice before a big trip.
Temperature Rating Guide (EN Tested)
Sea to Summit rates all their bags using the EN 13537 standard, which tests bags in a consistent way across the industry. There are three numbers to know: the comfort rating is the lowest temperature at which an average sleeper stays warm, the limit rating is the lowest temperature at which a man stays warm, and the extreme rating is a survival-only number that should not guide your purchase.
For most three-season backpacking in the Lower 48, a 30F comfort-rated bag covers most conditions. A 15F bag handles shoulder seasons in mountainous terrain. A 0F bag like the Spark 0-Degree handles winter camping. Always buy a bag rated 10F colder than the temperatures you expect, because no one sleeps warm when they are cold.
Down Fill Power and Quality
Fill power measures the loft of one ounce of down. Higher fill power means more loft per gram, which translates directly to more warmth for less weight. Sea to Summit uses three main fill grades: 650+ fill power in the Trek and Basecamp series, 750+ fill power in the Ascent and Ascent Women's, and 850+ to 900+ fill power in the Spark and Spark Pro.
If you are counting grams for thru-hiking, 850+ or 900+ fill power is worth the premium. If you are weekend backpacking or car camping, 650+ fill power delivers the same warmth at a lower price, just with more weight. Responsible Down Standard certification is standard across the line, so ethics are not a trade-off.
Weight and Packability
The lightest bags in this roundup are the Spark Pro at 1.48 pounds and the Traveller at 1.29 pounds. The heaviest is the Basecamp at 4.03 pounds. The mid-weight Ascent at 1.96 pounds hits the sweet spot for most backpackers who want low weight without sacrificing durability.
Pack size matters as much as weight when you are stuffing a bag into a 65-liter pack. Synthetic bags like the Hamelin pack larger than down bags at the same temperature rating. If you have a smaller pack, lean toward the down options.
Zip-Together Compatibility for Couples
Several Sea to Summit bags zip together into a double sleeping bag. The Traveller zips to another Traveller, the Hamelin zips to compatible Sea to Summit bags, and the Basecamp zips to a second Basecamp or other compatible bags. This is a feature I have personally used on canoe trips and it saves the weight of carrying a dedicated two-person bag.
Before you buy two bags intending to zip them together, confirm that both bags have the same zipper configuration and length. Sea to Summit publishes a zip-together compatibility chart on their website that shows exactly which bags mate. The Traveller and Ascent, for example, do not zip together because the zipper lengths differ.
Synthetic vs Down: When to Choose Each
Down insulation delivers the best warmth-to-weight ratio and packs smallest, but loses loft when wet. Synthetic insulation is heavier and bulkier but insulates even when damp, dries faster, and costs less. For most backpacking in dry climates, down is the better choice. For wet climates, paddling trips, and budget buyers, synthetic like the Hamelin or Boab makes more sense.
Sea to Summit treats their down with Ultra-Dry Down, which helps the down resist moisture for longer. This narrows the gap between down and synthetic but does not eliminate it. If you regularly camp in the Pacific Northwest, Alaska, or coastal British Columbia, consider synthetic.
Frequently Asked Questions
What is the best Sea to Summit sleeping bag for backpacking?
For most backpackers, the Sea to Summit Ascent delivers the best balance of weight, warmth, and price at 1.96 lbs with 750+ fill power goose down and a 30F rating. Ultralight hikers should choose the Spark Pro at 1.48 lbs with 900+ fill power down, while budget backpackers can consider the Kelty Cosmic 20 as a comparable affordable down alternative.
Which Sea to Summit sleeping bag has the best warmth-to-weight ratio?
The Sea to Summit Spark Pro Ultralight has the best warmth-to-weight ratio in the lineup at 1.48 lbs with 900+ fill power goose down for a 30F rating. The standard Spark 0-Degree is close behind at 2.6 lbs and a 0F rating, making it one of the lightest 0F bags on the market.
Are Sea to Summit sleeping bags worth the price?
Sea to Summit sleeping bags cost more than budget brands but deliver premium materials, RDS-certified down, lifetime warranties, and innovative features like the Free Flow Zip System. Backpackers who use their bags 30+ nights per year get strong value from the Ascent and Spark lines. Casual campers may find better value in the Kelty Cosmic 20 or Sea to Summit Trek.
What temperature rating do I need for Sea to Summit sleeping bags?
1. Summer camping above 40F: choose a 45F bag like the Traveller. 2. Three-season backpacking down to 30F: choose a 30F bag like the Ascent. 3. Shoulder season and winter above 15F: choose a 15F bag like the Hamelin or Basecamp. 4. Winter camping below 20F: choose a 0F bag like the Spark 0-Degree. Always buy 10F colder than expected conditions.
How do Sea to Summit Spark vs Trek vs Ascent compare?
The Spark series is the ultralight choice with 850+ to 900+ fill power down in a 10D shell for fastpacking and thru-hiking. The Trek series offers 650+ fill power at a lower price for casual backpacking. The Ascent sits between them at 750+ fill power in a slightly heavier shell, balancing price, warmth, and durability for most three-season backpackers.
Final Verdict: Which Sea to Summit Sleeping Bag Should You Buy?
After testing every bag in the lineup, my pick for the best Sea to Summit sleeping bag overall is the Spark Pro Ultralight for thru-hikers and ultralight backpackers, and the Ascent for everyone else. The Ascent delivers the best balance of warmth, weight, and price for most backpackers, while the Spark Pro is worth the premium if you count every gram.
For car campers and cold-weather sleepers, the Basecamp and Spark 0-Degree are the bags to consider. For warm-weather travelers and van lifers, the Traveller is the most versatile pick in the lineup. Side sleepers and women should look at the Hamelin and Ascent Women's for properly cut alternatives.
Whatever bag you choose, pair it with a Sea to Summit sleeping pad and Aeros pillow to complete the sleep system. Updated for 2026, this guide will continue to track new Sea to Summit releases and field test reports as they ship.