Sea to Summit Flame FmII Sleeping Bag Review

I’m going to start with a controversial opinion: I hate quilts. I think they’re uncomfortable, drafty, and don’t work well with foam sleeping mats. In contrast, I love the soft, warm hug of a completely enclosed bag. I’ve frequently complained that my ideal sleeping bag would basically be a down sock, that you can simply pull up or down rather than having to mess around with an ultralight zipper that snags on everything.

The Sea to Summer Flame FmII doesn’t quite meet this requirement, but it’s the closest of any sleeping bag I’ve ever used. A half-zip makes it easy to get in and out of but reduces the weight compared to a full zip. There’s no draft tube on the lower half, which cuts weight, but there are also no cold spots, so you won’t miss it. Quilt lovers will hate it though since there’s no option to unzip it completely and stick your feet out.

Outstanding warmth-to-weight ratio is my favorite thing about the Sea to Summit Flame FmII.

Sea to Summit Flame FmII Sleeping Bag At-a-Glance

Weight: 1 pound, 1.8 ounces
Length (regular): fits users up to 5’7”
MSRP: $379
Warmth Rating: 35°F/2°C
Compressed Volume: 2.9 liters

  • Fill: Ultra-Dry Down 850+ Loft
  • Shell: Ultralight 10D Nylon Shell
  • Liner: Ultralight 7D Nylon

Intended Use

I tested the 35°F bag, which would be perfect for summer conditions on most lower elevation trails. This sleeping bag is also available in 25°F and 15°F versions if you plan on using it at elevation or during shoulder season. At just over a pound for the 35°F version, it’s the ideal bag for someone with a low base weight who doesn’t want to switch to a quilt.

Circumstance of Review

I took the Flame on bikepacking, backpacking, and canoe camping adventures in Ontario, Canada over the course of two months. Due to sporadic local camping closures, I also used it in my bed at home to make sure I could really test for durability.

sea to summit flame fmii

A mummy hood and a zipper draft tube kept me cozy at low temperatures.


The Sea to Summit Flame FmII has Ultra-Dry Down 850+ fill. Essentially, this means the sleeping bag is warm for its weight, and lofts quickly once you remove it from its tiny stuff sack. Sea to Summit claims that Ultra-Dry Down retains over 60% more loft and absorbs 30% less moisture when compared with untreated down, and that their sleeping bags dry out 60% faster than untreated down bags. I certainly had no problems with condensation during my testing, even on cold, rainy nights. I also accidentally spilled water on my bag, and found that it didn’t soak through the shell at all. This makes the Flame a smart choice for wet environments like the Appalachian Trail if you don’t want to take a synthetic bag.

The 35-degree Flame features baffles in the torso and sewn-through construction in the leg area. Members of the Flame lineup that are designed for warmer temperatures are sewn-through in all areas, while the colder weather versions are fully baffled. I found the baffle construction on the 35F close to perfect. The sewn-through leg areas save weight, while the baffles around my core added warmth.

Read next – The Ultimate Guide to Backpacking Sleeping Bags and Quilts for All Budgets.



I requested the 35F bag, thinking that would be the perfect temperature for local summer conditions. Well, spring threw me a curve ball and the low on the first night was 40F. I’m normally a cold sleeper. I panicked that I was going to freeze. I considered taking a different bag. Instead, I paired the Flame with my winter sleeping pad and prepared to be cold all night. I was pleasantly surprised to wake up in the morning warm and toasty. Obviously, sleeping bag warmth is hugely subjective and depends on everything from your sleep clothes to how much you eat for dinner. However, I normally take a bag that’s 10-20 degrees warmer than the projected low, and I couldn’t believe how warm the Flame was, especially for the weight.

On other trips, I stuck to a much more sensible range of 50F-70F for nighttime lows. The Flame shines at these temperatures: I was neither too hot nor too cold.

sea to summit flame fmii

When compressed fully, the Flame is even smaller.

Compressed Size

The Flame fits into a tiny 3.5l stuff sack. It’s incredibly compressible, and lofts quickly once you remove it. I found the small size very useful for bikepacking, when gear volume often matters more than weight. For long hikes, I’d compress it a little less to avoid impacting the down, but it’s great to know that it can take up barely any space in your pack when you need the room for long food carries. It’s so small and light, I even throw it in my pack on day hikes for additional safety.


The warmth to weight ratio in the Flame series is outstanding. The 35F bag weighs just over a pound at 1lb 1.8 oz. Even if you want a warmer bag, the 15F comes in at just 1lb 15.4 oz. That’s a sub-two pound three season sleeping bag. Most ultralighters would be proud to have these bags in their packs.


I’m 5’2” and tested the regular, which fits users up to 5’7”. There was a small amount of dead air at the bottom of the bag, but not enough to make me cold. A 5’6” friend still found the bag long enough, so listed sizes are accurate. The bag has a slim fit, which helps keep the weight down. I found it was roomy enough that I could toss and turn, sleep on my side, and even stuff a small dog in there. However, if you like your sleeping bags baggy, you may want to consider a different style.


In a sea of purple and baby blue sleeping bags, I am so happy to see a women’s specific sleeping bag in grey and orange. Thank you, Sea to Summit, for not offering this in a “girly” color. The grey exterior helps to hide dirt, while the orange interior would be great for signalling in an emergency. My only slight nitpick about the appearance of the bag is that the thin shell material means you can see darker feathers through it. I’m more than happy to make this trade for dropping a few ounces by using lightweight materials.

sea to summit flame fmii

All testers approved of this sleeping bag.


It’s hard to truly review durability, since by the time I wear out a product, I’ve normally had it for a few years. However, I’m confident that the Flame would stand up to at least one full length thru-hike, if not more. I tested this bag with the help of Chester the dog, who definitely provides more wear and tear than a normal user. Despite Chester running over the bag and treating it like a dog bed, there were no snags or rips in the lightweight fabric, and there was zero feather loss.

While the Flame is durable, the stuff sack provided with it is not. On the second use, stitches audibly popped when I compressed the bag. Most hikers will want to swap out the stuff sack for a roll top waterproof bag for added water protection anyway.

Note the baffles vs. sewn through construction, which both adds warmth and cuts weight.

Sea to Summit Flame FmII Pros

Warmth to Weight Ratio: This bag is light, but still warm. That’s all most thru-hikers really want in a good sleeping bag, and the Flame absolutely knocks this out of the park. You might be able to find lighter or warmer bags on the market, but the Flame does an exceptional job of providing warmth at a low weight.

Tiny size: The Flame compresses down so small you’ll barely notice it in your pack. Unless you’re trying to downsize to a smaller pack, you might not care so much about compressed size for thru-hiking as long as it doesn’t take up half of your backpack. However, most thru-hikers also enjoy different adventure sports, and I found the tiny size translated exceptionally well to bikepacking.

Features: A draft tube and a hood on an ultralight sleeping bag are a bit of a luxury. While I don’t always love mummy hoods, I’m really excited to have a draft tube on the zipper to help keep me warm.

Read next – The Best Backpacking Sleeping Bags of 2021.

Sea to Summit Flame FmII Cons

Zipper: Almost every single ultralight zipper I’ve ever used is sticky and difficult to work. Unfortunately, the Flame falls prey to this flaw, too. I found the zipper difficult to unzip when I was fully inside the bag, although zipping it up was much easier. I normally just push my sleeping bags down to get out of them, so this wasn’t a deal breaker for me.

No option to completely unzip: As already discussed, this is not a bag for quilt lovers. You can’t unzip fully if it’s too warm. You can’t poke your feet out of the bottom. This is my absolute favorite feature about this bag, but many people will hate it. If you like quilts, you will hate this bag. If you don’t like quilts? You’ll love it.

Price: The Flame is a little spendy in comparison to some other sleeping bags, although its low weight justifies this. If you’re thru-hiking, it’s well worth paying to drop a few ounces from your big three. If you’re just starting out, or only hike a few times a year, the price may be a deal breaker.


The Flame competes with cottage brands in terms of warmth to weight ratio, but provides more features than some comparable lightweight bags (such as a draft tube over the zipper, and a mummy style hood). My bag was donated for this review, but I’d happily spend my own hard-earned money on it. This is about to become my go-to summer sleeping bag.

Shop the Sea to Summit Flame FmII

A Few Comparison Items

NEMO Disco 30 Women’s Sleeping Bag 

  • MSRP: $259.95 (for regular)
  • Weight: 2lbs 5oz
  • Temperature Rating: 30F
  • Insulation: 650-fill-power PFC-free down

Marmot Hydrogen Sleeping Bag: 30F Down 

  • MSRP: $340.95
  • Weight: 1lb 7.3oz
  • Temperature Rating: 30F
  • Insulation: 800-fill down, Down Defender treatment

Western Mountaineering Caribou MF Sleeping Bag: 35F Down

  • MSRP: $375.00 (for 5’6” bag)
  • Weight: 1lb 4oz
  • Temperature Rating: 35F
  • Insulation: 850-fill goose down

The Sea to Summit Flame FmII was donated for purpose of review.

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Comments 2

  • Debra Harvey : Jun 25th

    A great review. ?

  • JhonYermo : Jun 25th

    $379 for 32º ?? Yeah sure, you bet. And a fart sack. Just NUTS


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