Sea to Summit Flame III Review

February 27, 2019
Sea to Summit Flame III
Sea to Summit Flame III SeatoSummitFlame_01 SeatoSummitFlame_02 SeatoSummitFlame_04 SeatoSummitFlame_05 SeatoSummitFlame_06 SeatoSummitFlame_08 SeatoSummitFlame_09 SeatoSummitFlame_10

The Good

  • Packs small
  • Very warm and comfortable
  • Lightweight
  • Hydrophobic down

The Bad

  • Expensive
  • Lightweight materials seem fragile
Our female testers loved this bag. It is lightweight, fluffy, very warm, and packs super small. The hydrophobic down makes it even more versatile and reliable and the fit and cut, which is wider in the hips and narrower at the shoulders, is ideal for the average lady. Its EN warmth rating is for higher temperatures than any other bag in this three-season test, but the weight and bulk remain among the lowest. The fact that it comes with an excellent compression sack that squishes the bag into a tiny bundle is a bonus. For women in search of a three-season bag for backpacking, this one comes highly recommended.

The Sea to Summit Flame III is a new product for 2019 and is the only women’s specific bag we have included in this review. In general, men and women can use the same sleeping bags as long as they are sized appropriately for height. The benefit for women when it comes to buying a women’s specific sleeping bag is that these bags are often shorter (meaning less weight and bulk as well as less cold spots), wider in the hips and narrower at the shoulders (which equals a more comfortable fit, especially in a mummy bag), and they often have a little more insulation packed into them than an equivalent unisex bag (because women often sleep colder than men). All of these things are true with the Flame, and our female testers felt that this bag fit better and was more comfortable than many of the unisex bags in this test.


The Flame III is listed as weighing 1 pound 8 ounces. On our scale, it clocked in at 1 lb 7.8 oz, so just under the manufacturer weight. This is slightly heavier than the featherweights in this review: The Z Packs Classic (1 lb, 3.2 oz), the Therm-a-Rest Vesper (1 lb, 3 oz), and the Feathered Friends Tanager (1 lb, 2.6 oz). However, none of those bags have hoods! If you want to include warmth of a hood, four extra ounces is not a high weight price to pay. This is the lightest hooded bag in our review, though this is a women’s bag, meaning it is also a little shorter than the average unisex bag.


This bag packs into a tiny package. It comes with an excellent compression sack, which is always a bonus in our opinion. And this sack is nice and small, which forces the user to stuff the bag down to a very small size. We admit that at first in our testing it was a challenge to get this lofty, fluffy bag into the small sack—but we are not complaining. We love the fact that this bag is warm and made with high lofting down, and we love that it can compress down so small. When backpacking, using a bag like this is incredible because the sleeping bag no longer takes up a majority of the space in a backpack. These keeps our packs small and leaves room for a few small luxury items.


The Flame is rated for 25ºF, which is a little higher than most of the other bags in this review, but it helps to look at this rating a little more closely. The Flame is European Norm (EN) rated, which is an industry accepted standard for rating the warmth of sleeping bags. With this standard, bags are given two different temperature ratings, the Comfort rating, which is the lowest temperature that a “cold” sleeping will feel comfortable and a Lower Limit rating, which is the lowest temperature that a “warm” sleeper will be comfortable. Though it is not always the case, the difference between a “cold” and “warm” sleeper tends to divide along gender lines. Women often sleep colder and men typically sleep warmer. Because of this, many manufacturers will use the Comfort rating as the primary temperature rating on women’s bags and the Lower Limit rating on men’s or unisex bags, because those are the numbers most applicable to the average consumer.

The Flame is, uniquely in this review, a women’s bag. So, the 25-degree rating is the Comfort rating, which is why it looks like it is designed for warmer weather than other bags in this test, which are all rated around 20-degrees. If we look at the Lower Limit rating, the Flame is a 14-degree bag. To compare, the unisex Therm-a-Rest Vepser has a Comfort rating of 32 and a Lower Limit rating of 20 and is therefore marketed as a 220-degree bag. Likewise, The North Face Hyper Cat has a Comfort rating of 30 and a Lower Limit rating of 24, and yet it is marketed as a 20-degree bag. And the ZenBivy Bed has a Comfort rating of 34 and a Limit rating of 23. If comparing the EN ratings, the Sea to Summit Flame is actually warmer than most other bags in this test.

But how does this translate to use in the backcountry? In our experience, this bag was satisfactorily warm. We used it on cool summer nights at high altitudes in the High Sierra and were extremely happy with how it performed. Our tester felt that she would be happy with this as her one bag to bring with her for almost all backcountry camping trips and plans to replace her old three-season bag with this one. In a less subjective way of assessing the warmth of the bag, we took a peek at fill weight. This is the weight of just the insulation that goes inside a bag. The regular length Vesper has 12.6 ounces of down, the Classic has 13.1 ounces of down, and the Flame has 16 ounces of down- and that is in a slightly shorter bag. This women’s bag really is packed with a bit more feathers than the rest.


With all the things we love about this bag, the low weight, the great compressibility, the warmth, there isn’t much to write home about in terms of ventilation. That’s not necessarily a bad thing, it depends what the customer is looking for. There are now many quilts and non-traditional bags on the market, like the ZenBivy Bed, that cater to those who want more freedom and fresh air in their sleep system. The Flame is a standard mummy bag, with a full-length side zipper that can be undone when it gets stuffy inside. It does have 2 sliders to offer different venting options. This is more efficient than the half-length center zipper on The North Face Hyper Cat, but it is not as open as the Z Packs Classic bag or the Therm-a-Rest Vesper. We think that the standard mummy shape is the most efficient use weight to stay warm, so on cooler nights, we like this shape.


As with most lightweight products, the feature set on this bag is simple. It has a side sipper and a hood with a cinching drawcord. The hood also snaps to the top corner of the bag to keep it sealed tightly against cold. There is a fluffy draft collar around the hood and a draft tube next to the zipper.

Other slightly less obvious features are the fact that this bag is fully box-baffled, so none of the seams are sewn-through, which eliminates cold spots. The baffles along the chest are vertical, which prevent the down from sliding around and getting stuck on the underside of the bag. Both of these things contribute to the warmth and function.

Finally, the down is treated with a hydrophobic coating. Sea to Summit’s Ultra Dry down gives the feathers more resistance to moisture, whether it is condensation from the inside or drips from the outside. This makes the bag more resilient in wet weather. We don’t think that it holds up quite as well as synthetic insulation in a downpour, but this type of treatment does extend down’s usefulness and weather resistance.


In our testing, the Flame III has held up well. The one area where it could suffer is durability. It is constructed with ultralight materials, which obviously keeps the weight desirably low. The shell material is a 10-denier nylon and the interior lining is a 7-denier nylon. Both of these are more fragile than a robust 20-denier material (but you wouldn’t want to carry a sleeping bag made out of that!) We had zero durability issues with this bag or these materials during our testing period, but we suggest treating this bag with care.



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