Gear Review: Sea to Summit Flame UL Women’s 15-Degree Sleeping Bag

The Sea to Summit / Flame UL Women’s (15°) is a warm, ultralight mummy bag. There are no unnecessary features like mat attachments or extra zippers. Instead, it is made of high-quality down and lightweight, water-resistant fabric meant to keep you warm, dry, and not be too heavy in the pack.

Basic Specs

MRSP: $529

Bag Weight1 lb 15.4 oz / 840 g
Compressed Volume7.1L
Compression SackS – 10L to 3.3L
Fill weight22.9oz/650g
Fits up to5’7” / 170 cm
Season Rating3 season
Women’s Temp (EN Rating)15°F / -10°C

image via

Note: This comes in Regular and Long length options. I was disappointed that they did not have a petite option, but upon receiving the sleeping bag, I am glad I did not get a smaller one. I am 5’4” and did not find that there was too much excess room in the footbox.

Circumstance of Review

I took this bag out on several trips throughout the summer of 2019 in northern Ontario, Canada. This included overnight backcountry canoe and hiking trips in Algonquin Provincial Park.

The weather was clear on all of these trips and warm. I wanted this sleeping bag for shoulder season camping more than summer, so I did take it out in early November to test out the comfort level in temperatures closer to its rating (approximately 3°C/37.4F). I will be taking it out in below-freezing temperatures this winter, so stay tuned for an update here with winter results.


When you’re fully zipped up into the bag with the hood pulled up around your head, it’s a cozy cocoon. This women’s bag is narrower at the shoulder and wider at the hips in order to give the best possible fit for women. The down is distributed with a specific focus on the footbox and torso areas. The 15F bag has a full-length zipper down the right side.


The zipper is held in place at the top of the bag by a small button.

This bag uses ULTRA-DRY Down 850+ Loft 90% Down Cluster Premium Goose Down, which is the highest-loft down used in any of Sea to Summit’s series of sleeping bags. The shell is made of 10D UL Nylon while the interior is 7D; these materials are lightweight and durable with a Durable Water Repellent (DWR) coating intended to shed excess moisture. The zippers are small and lightweight as well.

Sea to Summit sleeping bags use down certified under the Responsible Down Standard (RDS). The RDS is an independent standard that ensures sustainability and ethical conduct for down products and it was designed with input from animal welfare groups, industry experts, brands, and retailers.


This sleeping bag is extremely warm and cozy. The coldest temperature I’ve taken it out in so far was around 3°C/37°F, and I was warm and comfortable all night. On warmer nights, I unzipped the bag to allow some heat out and for more freedom of movement. It is also extremely light with an impressive warmth-to-weight ratio. So far, the materials have held up well to everything I’ve put it through. It has shown no sign of wear; most importantly, no loss of down loft.

I found it a comfortable sleep, not too constricting. This is likely due to the extra space in the hips that comes from the customized shape for women. I was very pleased with the length as well—being short means that a lot of my gear (sleeping bags, tents) are too big for me, and excess material means excess weight in my pack. The Regular size fits a person up to 5’7”, the Long version is not yet available (the Sea to Summit website lists it as “Coming Soon”) but will be for a person up to 5’10”.


Couples take note. This bag is not designed to be zipped into another sleeping bag.

For me, the biggest downside to this sleeping bag is how small it packs down (hint: it doesn’t really). It comes with a manufacturer stuff sack, with buckles on it, which does not appeal to my ultralight inclinations. Usually, I store my sleeping gear (bag/quilt and my sleeping mat, a Big Agnes Q-Core SLX) in a Sea To Summit Ultra-Sil 20L dry bag. I did this the first couple of times that I packed out the Flame mummy bag, and no matter how small I would compress the bag when packing it, it would expand to be enormous. Generally, that dry bag would take up half of my 40L pack.

Left: Manufacturer stuff sack; Right: Ultra-Sil 20L Dry Bag with sleeping bag packed in it.

The 20L Ultra-Sil bag weighs 1.8 oz, compared to the manufacturer sack (buckles and all), which weighs several ounces more, but allows you to cinch the bag to a much smaller size. Sea to Summit does offer an ultralight version of the default sack that weighs 2.3 oz for the 10L bag. Don’t forget that you shouldn’t store a sleeping bag compressed in a stuff sack. Instead, store it in a loose, breathable bag.

Comparable Bags

For the sake of comparison, I’ve selected three other mummy bags for women and a unisex quilt, all rated for 15F. The Flame IV weighs a full pound less than the Big Agnes and Marmot mummy bags; in fact, its weight is comparable to the Katabatic quilt. This is an impressive feat for a sleeping bag with full zippers, but not a feature that is unique to Sea to Summit. For example, the Sierra Designs mummy bag listed below has a comparable temperature rating and weight at a much lower price point.

Sea to Summit Flame fmIV 15 Marmot Teton 15 Sleeping Bag WBig Agnes Hazel SL 15 Sleeping Bag WSierra Designs

Women’s Nitro 800 / 20 Degree

Katabatic Flex 15
Temp Rating15 F15 F15 F17 F15 F
Weight1 lb. 15 oz.2 lbs. 15.5 oz.2 lbs. 12 oz.1 lb 11 oz1 lb. 9.1oz

Note: This is in no way a comprehensive summary of mummy bags available or a review of the quality of other bags listed in this table. It is simply meant to illustrate a range of bags/quilts with similar features.


“All Sea to Summit products carry a lifetime warranty against defects in workmanship and materials to the original owner for the intended life of the product under normal use…this excludes normal wear and tear and material breakdown due to age, use, or environmental conditions.” Details about returns, warranty claims, and repairs can be found here.


Generally, I’ve been an avid proponent of quilts for ultralight backpacking. However, we seem to have reached a point where technical materials are so good that you can have a warm, durable mummy bag with full zipper and hood come in weighing less than two pounds. So as long as I have the proper stuff sack to cinch it down to a reasonable packed size (yes, I’ll probably invest in the ultralight version), this is going to be a staple of my gear for shoulder season camping (and probably some winter camping too).

This bag is of high quality and is toasty warm. I would trust this bag to keep me warm well into the lower end of its temperature rating range. It’s specially made to fit women’s bodies and keep heat in the areas where it is needed. However, it is likely out of most hikers’ budgets. If you can afford to pick it up, it’s a high-quality bag. If it’s out of your budget, there are significantly cheaper bags with similar stats.

Shop the Flame UL Here

This item was donated for purpose of review

Affiliate Disclosure

This website contains affiliate links, which means The Trek may receive a percentage of any product or service you purchase using the links in the articles or advertisements. The buyer pays the same price as they would otherwise, and your purchase helps to support The Trek's ongoing goal to serve you quality backpacking advice and information. Thanks for your support!

To learn more, please visit the About This Site page.

Comments 2

  • Ellie : Nov 12th

    thanks so much for this thorough review! I’d saved the bag in a tab for potential black friday reductions, but i might have to check out the Sierra Designs


What Do You Think?