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Home » Mountain Standards » Sea to Summit Flame IV: A warm ultralight sleeping bag tailored specifically for women

Sea to Summit Flame IV: A warm ultralight sleeping bag tailored specifically for women


MSRP: $529

Every female ice climber I know gets colder than the “dudes.” I remember working on a story about one of the best female ice climbers in the world and I ran into one of her partners at a base of a climb. I asked him for a fun quote about her and he said “she can wear more jackets than anyone I know.” I laughed, because I myself was wearing many jackets and had just had the worst “first-climb of the season barfies.” It was only November and barely below freezing.

A range of studies over the years have shown that women are more likely to be sensitive to cold temperatures than men. Many of these studies cite variables such as musculature, metabolic rates (which correlate to musculature), blood circulation and subcutaneous fat. Results seem to agree that it can take longer for women to warm or cool their core temperature and that their extremities may be more vulnerable to the cold.

Because of this, getting the right sleeping bag for the right objective has often been a challenge for me and most of my female friends. A friend, who had her apprentice ski exam this spring, asked to borrow my -40F/C bag. I thought it was a little excessive for the Selkirks in April, but I knew where she was coming from–she really couldn’t risk being cold and not getting a good night’s sleep. Sea to Summit understands this struggle: their new Flame Women’s Ultralight Down Sleeping Bag is their answer.

The Flame comes in four models and an insulated liner that range in price from $229 to $529. This series of sleeping bags covers a women-specific temperature rating of 48F to 15F (9C to -10C) and are designed to be paired with other bags for extra warmth, but cannot be coupled/zipped with other sleeping bags. I tested the Flame IV, which has a “women’s temp rating” of 15F/-10C. It is made with mapped baffles designed for a woman’s body to maximize heat retention, and from my experience being a “constantly cold” woman, Sea to Summit accomplished their goal.

The weight and packability of the Flame series help make this a worthy design. Have you ever brought a bag on a trip and it takes up so much space in your pack that you question bringing it on your next outing? Thus, you bring a lighter, lower-rated bag on your next trip because of the space and weight, only to regret your decision as you lie awake with an aching neck and back, scrunching your shoulders to make yourself warm? There is a reason the world is obsessed with weight, but for those who have made the above mistakes, the common move is to just give up and get a bigger pack. According to Sea to Summit, the Flame, however, is designed to pack down smaller than other bags in its weight. An Outdoor Gear Lab article titled “The Best Sleeping Bags for Women of 2019” shows that the Flame has a warmer rating than 15 other bags and is lighter than most of them, though there are some that are rated to around 20F and are slightly lighter.

My testing of the Flame IV has been limited because of a recent surgery that curtailed my activities, but I was able to take it out for a cold night of camping in the Purcell Range at an elevation of about 1100 meters (around 3,608 feet). The temps were approximately -7C to -10C (19F to 15F), which is the exact rating of the Flame IV (-10C/15F).

The author posing with the Sea to Summit Flame sleeping bag, which is made specifically for women. [Photo] Katherine Erwin collection

The author’s friend holds the Sea to Summit Flame IV sleeping bag, which is made specifically for women. [Photo] Kate Erwin

Within minutes of setting up my tent and rolling out my bag, my black Labrador, Zelda, came in and made a hole in the sleeping bag. She is affectionately called “Zelda Krueger” because her claws resemble the horror film character Freddy Krueger and she wreaks just as much havoc. I don’t fault Sea to Summit for this, because Zelda has previously torn ripstop fabric that was stronger than 10-denier, which is what the Flame’s shell is made out of. In the future, I will be more cautious with the face fabric of the bag. I easily mended the hole with some vapor barrier Tuct Tape.

When handling the Flame, it is clear where Sea to Summit has added more concentrated insulation. The 850 fill baffling around the chest area runs vertically and is noticeably plumper than the rest of the bag. The fill is made of 90 percent down cluster of premium goose down–Responsible Down Standard (RDS)–and has been treated with water-repellent. The bag only weighs 890 grams but “sleeps” heftier; it feels like an old 11.6F/-11.3C Brooks Range bag that has been my go-to for anything below 20F (-7C).

When I first fell asleep in the Flame IV, I didn’t notice the hood cinch, (the toggle is on the left side, opposite of the zipper). This didn’t seem to matter since there is so much loft in the hood and neck collar area that I could almost fold it over my face for coverage.

I wasn’t warm when I first got in the Flame, but later I noticed–after barking dogs woke me in the night–that I was very warm and comfortable. I instantly went back to sleep and got into a deep REM. I was wakened a second time–not for lack of comfort but yet again by barking dogs–and it was then that I noticed that I was actually feeling too hot in the chest area, but not sweaty hot. I found that the bag was rather breathable with the heat. I took off a layer to regulate.

I could easily move around in the bag, although, like every sleeping bag I have slept in, it does twist with you. In spite of all this movement, the zipper stayed zipped.

Lastly, the socks DID come off–which is the highest compliment to any sleeping bag if you have been susceptible to cold nights and cold toes, as I have.

Kate Erwin has been getting cold in sleeping bags in the Northeastern US since she started climbing in high school. She took a bit of a hiatus to work in the fashion world, then motorsports, but decided that being cold and swinging axes in the Canadian Rockies is more fun than fast cars, and that technical gear is much more useful than stylish duds. You can see more of her work at

Designed for women
Warm (rated to 15F/-10C)
Lightweight (890g/1lb. 15.4 oz. for regular length)
Packs down easy even without the compression sack, which has a volume of 7.1L for regular length)

Sticky zipper
Can’t “be coupled” (zip together) with another bag