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Sea To Summit Flame FmIV Sleeping Bag 2024 - 2022 Review by The Good Ride

Sea To Summit Flame FmIV Video And Written Review

The Sea To Summit Flame FmIV is an ultralight down sleeping bag that comes in a variety of different temp ratings. I tested the 15F bag in a women’s regular size.

Ethics Statement: We don’t get paid by the manufacturer to write these reviews.  No one is perfect and we do make money from the “Where To Buy” links below, but this is our best attempt at an honest and objective review from an average camper’s perspective.

Testers: Steph

Sleeping Conditions: I tested in low 20F nights. The mornings were quite humid, with a freezing fog that came in around 3am.

Steph’s Specs

Height – 5’3″

Weight – 108lbs

Shoulder Width – 16”

Hip Width – 17.5″

Size: Women’s Regular

I felt like the women’s regular fit bag worked well with my specs. There was just enough room to move around a bit, but it was snug enough to keep the warmth in.

Women’s Regular Bag Specs

Height 5’7″

Bag Circumference

Shoulders 57″

Hips 54″

Feet 35″

Weight (For the 15F Bag) 1lb 15.4oz


Ultra-Dry Down 850+ Loft

Temp Ratings Available

48F, 35F, 25F, 15F, Liner

Prices Range From $289 – $609

I was very surprised at the loft the bag had. It fluffed up nicely after being unpacked out of the compression bag. The amount of loft the Flame FmIV had added to the comfort and warmth of the bag while sleeping in it.


Outer Shell Ultralight 10D Nylon

Inner Liner 7D Nylon


This bag comes with a hood that creates a nice layer around the head and neck to add warmth while sleeping. The colder temp bags have an extra collar around the neck as well. The hood has a drawstring to cinch down the hood around the head.

The Flame IV also comes with 4 attachment loops to make attaching a quilt easy for added warmth in colder temps.

There is a reversible zipper so you can vent the feet, or unzip the bag altogether.

Women’s Specific Design

The shape of the women’s Flame bag is narrower in the shoulders, and has added room in the hips and knees.

The insulation body mapping is different in the women’s bags compared to the men’s bags. Adding more warmth in different areas.

Zip Compatibility with other Sea To Summit Bags

The Flame FmIV is compatible to zip to another Flame bag or Spark bag to create a double sleeping bag. This is great, I love the ability to combine two different temp ratings as well. So you don’t need an extra bag when you camp with someone else. You can have the bags separate or together.


I found the Flame FmIV very comfortable. The loft and shape helped a lot with this. It has a contoured mummy fit, but without being too constricting. The hood has a nice fit, and keeps the cold air from coming around the neck and shoulder area. I liked the sizing for my specs as well.


I tested this bag with the Sea To Summit Ether Light XT Insulated Sleeping Pad. 

Normally, I run very cold during the night and just have learned to deal with it while camping. I always sleep in a down jacket, and put a hot water bottle at my feet for added warmth. I did neither of these when testing these sleep systems. And I was quite nervous to sleep without my backup warmth but committed to sleeping in normal layers to see if everything kept me warm. It was amazing to actually be comfortable most of the night. The only time I got cool feet, was at 3am when the fog rolled in and temps dropped for a couple hours. But I still stayed warm enough to continue sleeping.


The Flame FmIV comes with a compression sack to pack it in. It takes a little effort to get the bag packed away but it isn’t too bad. This bag packs down to a compact size that is pretty good with the amount of warmth and insulation the bag has.

It also comes with a nice storage bag that keeps the insulation lofted while not in use.


The Sea To Summit Flame FmIV comes with a lot of warmth, comfort, and packs down to a decent size for backpacking. It has a lot of good features that are all useful and nothing that you don’t need. They kept the design simple and to the point. I like that it comes with it’s own compression sack and a pretty nice storage bag as well. I was happy with the fit and warmth when I used the bag, and feel the temp rating was accurate.

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Sea To Summit Flame FmIV Sleeping Bag Specs

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Sea To Summit Flame FmIV Sleeping Bag User Reviews

Where To Buy

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Sea To Summit
Flame IV Ultralight 15F
$589 Buy it

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