Sierra Designs’ Ultralight sleeping bag series consists of six bags with a similar design. Four are 800-fill down insulated and two are insulated with Primaloft Sport. These bags have an essential feature set, yet are made as light as possible with 20-denier fabrics, a small jacket-style hood, and a half-zipper. The Flash is the warmest of the four down bags. It’s rated by the maker at 0 °F, yet weighs only 2 pounds 12 ounces in size Regular. It’s also a good value for a zero degree bag at $390. How well does the Flash perform as a winter sleeping bag, and is it suitable for milder conditions?
- Lightweight, downproof shell fabric is soft and supple
- 800-fill down
- Baffled construction
- Parka style hood
- Footbox vent
- Draft collar
- Dual draft tubes
What’s Not So Good
- Curved zipper is hard to zip
- Half zipper and foot vent do not provide enough ventilation for comfort in warmer temperatures
|2007 Sierra Designs Flash|
|Mummy with ½ zipper|
|Bag, lightweight stuff sack, mesh storage bag|
|800 down; 28 oz (794 g) size Regular, 30 oz (850 g) size Long|
|3.75 in (10 cm) single layer loft in chest area, 3.25 in (8 cm) in hip and leg areas|
Manufacturer Claimed Temperature Rating
|0 °F (-18 °C)|
|9 in x 19 in (23 cm x 48 cm)|
|Measured weight size Long 2 lb 12.2 oz (1.25 kg); manufacturer specification 2 lb 15 oz (1.33 kg)|
|Regular (to 6 ft, 1.82 m), Long (to 6 ft 6 in, 1.98 m)|
|Shell 20 d polyester with DWR, lining 20 d polyester|
|Jacket hood, dual draft tubes, draft collar, ½ length zipper, snag-free zipper track, fixed side baffle construction, zippered footbox vent, removable pad straps|
|$390 Regular, $404 Long|
The Sierra Designs Flash is listed as a men’s sleeping bag and is available in size Regular (fits to 6 feet) and Long (fits to 6 feet 6 inches). Their catalog does not show a comparable women’s model with the same temperature rating.
The Sierra Designs Flash is designed and constructed to minimize weight: 20-denier shell and lining fabrics, jacket hood, half zipper, high-loft down, and a trim cut.
According to Sierra Designs’ specs, the size Regular Flash contains 28 ounces of 800 fill-power down and size Long contains 30 ounces. We appreciate this disclosure; some manufacturers won’t disclose how much down is in the bag! Sierra Designs’ choice of 800 fill down appears to be a good balance of quality down and value. Nowadays 750 fill down is considered an entry level for a lightweight sleeping bag, and 850 fill or higher down is considered high-end, where you are clearly paying a premium for the weight savings it provides. So Sierra Designs’ use of 800-fill down is nothing to sneeze at; it's good high-loft down, and certainly adequate if the bag construction and price are right.
The Flash has fixed side-baffle construction, which holds the down in place for uniform loft. It does not have the ability to shift down as with continuous baffle construction. I measured the bag’s loft in several places and found it has an average of 3.75 inches of single-layer loft in the torso area and 3.25 inches in the leg area. These loft measurements translate to an estimated -10 °F temperature rating, according to our table included in the Backpacking Light Position Statement on Sleeping Bag Temperature Ratings. Based on loft, the Flash is fairly rated, but many factors affect sleeping bag warmth, as the referenced article points out.
Ultralight backpackers are finicky about sleeping bag weight. If a bag is underweight, they worry that it was shorted on down fill; if it’s overweight, they complain that it was misrepresented. The Sierra Designs Flash I tested (size Long) is 2.8 ounces underweight, but based on the consistent loft measurements and evenly filled baffles, it does not seem to be underfilled.
The Flash has a 35-inch long half zipper. It begins on the left side of the bag and ends at the left side of the hood (see previous photo). Inside, there is a puffy draft tube on each side of the zipper plus a two-part draft collar that connects with Velcro. There are two drawcords inside; one draws up the draft collar and the other draws up the front of the hood.
The shoulder, hip, and foot girth of the Flash is trim at 60, 57, and 40 inches respectively for size Regular. A trimmer sleeping bag is definitely warmer, because you don’t have to warm up any extra space and there’s less of a bellows effect causing heat loss, but it’s a balancing act between slimness and having adequate room inside the bag so you don’t compress the down. I opted to get size Long (62-59-42) for the extra girth. I’m glad I did, as I will explain later. I’m not a real big person (6 feet, 170 pounds), but I typically wear some insulated clothing inside a sleeping bag so I don’t have to dress when I need to exit the tent in the middle of the night.
The outside shell and inside lining fabric are a 20-denier tightly-woven polyester sourced by Sierra Designs. It is very similar to nylon Pertex Quantum in its weight, suppleness, downproofness, and water-repellency.
The Flash’s Jacket Hood (top left) is exactly what it says. It’s shaped like the hood on a down parka, is well insulated, and has a drawcord on the front to draw it up. At the foot end there is a zippered foot vent (top right) to provide ventilation on warmer nights. The bag comes with two detachable pad straps (bottom left) to hold a sleeping pad in place. When stuffed into its ultralight stuff sack (bottom right), the bag compresses down to 9 inches x 19 inches, which can be further stuffed in the bottom of a backpack.
I mentioned that the Flash has a trim fit, and I opted to get a size Long mainly for the extra two inches of girth. For me, that was a good decision. Even though the Flash has a “snag-free zipper track,” the zipper does not operate smoothly. Rather than a smooth, continuous zip to close it, I had to close it in increments which took up to several minutes. The problem is caused by the bag’s trim fit, puffy draft tubes, and the pad straps. The snug fit and pad straps pull the zipper apart and the draft tubes get in the way. The upper part of the zipper, where it curves up to the left side of the hood, was especially hard to close. Because the pad straps made the zipper harder to close, I stopped using them after my first trip with the Flash, and had no problems with rolling off my sleeping pad.
The bag’s pad straps (left) increase the difficulty of closing the zipper. Beyond the pad strap attachment (right), the zipper binds even more on its upward curve toward the hood (right). The zipper is also difficult to open.
The full process for sealing myself up into the Flash is as follows: 1) close the zipper (it helps to pull up while pulling) and secure the Velcro tab at the end of the zipper, 2) inside the bag, secure the Velcro tab to connect the upper and lower parts of the draft collar, 3) snug the drawcord on the hood, and 4) snug the drawcord on the draft collar. Frankly, I found it a bit claustrophobic to be so tied into the sleeping bag, and I felt a bit panicky when I wanted to get out in the middle of the night and couldn’t find the drawcords, Velcro tabs and zipper pull, then found that the zipper is almost as difficult to open as it is to close. After using the bag on a few trips, my preference was simply to close the zipper and snug the drawcord on the hood. I advise practicing this process at home several times before using it in the backcountry.
The Flash’s Jacket Hood makes the sleeping bag fit like wearing a thick down parka. The drawcord on the front of the hood snugs it down to a small breathing hole, if desired. An advantage of this design is the hood stays in place when I roll over at night (when not using the pad straps). The bag rolls with me, rather than me rolling inside the bag.
I tested the Flash while igloo camping and winter tent camping in the southern Rockies. Low temperatures inside the igloo only got down to 30-32 °F, so it was easy to stay warm in the Flash. On my first trip I put the Flash inside a lightweight bivy to make sure it stayed dry. That was a mistake because I had lots of condensation inside the bivy which in turn dampened the sleeping bag. I weighed the bag when I got home and found it gained 3.1 ounces of moisture. On subsequent trips I skipped the bivy so moisture could escape more readily. Still, it gained about 2 ounces of moisture each night I slept in it, which highlights the need to air out a sleeping bag (in the sun) every day when winter camping.
Sleeping in the Sierra Designs Flash inside an igloo. (Note the “ultralight” stove - a luxury permitted by igloo camping.)
I also slept in the Flash while winter tent camping and stayed warm down to 14° F, and again at 4 °F. On those trips I wore some insulated clothing (a baselayer plus a Bozeman Mountain Works Cocoon pants and Montbell Alpine Down Jacket) inside the bag for convenience so I don’t have to dress to go outside the tent in the middle of the night. The size Long bag, with 62 inches of shoulder girth, has adequate room for me to wear clothing inside, but the extra bulk makes the zipper closing operation even more tedious. I have a low body fat level and get cold fairly easily, but I had no trouble staying warm inside the Flash under these conditions. However, many factors affect sleeping bag warmth, and your experience may be different than mine.
To test the bag’s foot vent feature, I slept in the Flash in a tent on a 55 °F night. I left the zipper open the first part of the night, and zipped it up toward morning. I found the foot vent provides some extra ventilation, but not a lot because the bag’s puffy walls tend to seal it up. It helps to hold the vent open with my toes to increase air circulation. The foot vent is not large enough to pass my feet through it and stand up with the bag on.
The Sierra Designs Flash sleeping bag is built for warmth. Its 3.75 inches of single layer loft in the chest area, in concert with puffy draft tubes and draft collar and a hood like an expedition parka, translate into a seriously warm 0 °F sleeping bag. It’s at its best in really cold temperatures down into the teens and single digits, and will achieve its comfort rating with only a few insulating clothes worn inside, which I normally do anyway. In warmer temperatures, its half zipper is only partially compensated by its foot vent, so the bag is simply too warm (for me) under more temperate conditions. A full length zipper would allow the bag to be used more like a quilt in warmer temperatures, and temperature adjustment would be easier.
The difficult to close (and open) zipper and snug fit are my key issues with the Flash. What would appear to be an elegant design - a distinct zipper channel curved up to the hood for easy closure- simply did not operate smoothly in practice. It was repeatedly a struggle to get it closed, and just about as difficult to get it opened. The snug fit exacerbates the zipper problem. Getting completely settled into the Flash is like putting on a flight suit, and the user is well advised to practice at home before attempting to do it in the dark, in the middle of the night, with an urgent need to urinate.
The Sierra Designs Flash is comparable with the Western Mountaineering Kodiak, which is also rated at 0° F. The Kodiak in size Long has 32 ounces of 850+ fill down, 3.5 inches of single layer loft, full-length zipper, and weighs 2 pounds 15 ounces (the same as the Flash). However, its shoulder-hip-foot girth is 67-58-41 inches, which is 5 inches more at the shoulders and about the same otherwise. The extra girth requires extra down, as evidenced by the 3.5 inch loft, which is about the same as the trimmer Flash. The Flash costs $76 less than the Kodiak, but the Kodiak is roomier and perhaps more versatile because of its full-length zipper.
The Flash has a hood that looks and fits like the hood on an expedition down parka. The bag fits like a sarcophagus; Sierra Designs should consider offering a gold-and-lapis option!
Recommendations for Improvement
- Re-design the zipper so it operates more smoothly
- Increase the shoulder girth