Sleeping Bag Guide
Sleeping bags can sometimes be confusing and difficult to understand. While we sure don't want to sound like we have all of the answers, we will review some of the key components of a sleeping bag... the insulation, the construction, the fabrics, the zippers, and the bag shapes... and hopefully explain them in terms you can clearly understand.
The main goal of any insulation is to provide as much "air" or "loft" as possible. Trapped, non-moving air is the best insulator, so it's the goal of the insulation to trap as much air as possible. Until the introduction of micro-fiber insulations, it was generally accepted that "loft was warmth"... in other words, more loft meant more warmth. Now micro-fiber insulations have the ability to trap more air in a smaller (less bulky) space, somewhat throwing a curve into the "loft is warmth" argument, but we'll discuss that more later.
So, if we were going to divide sleeping bag insulations into 2 general groups, it would be "natural" (down) and synthetic. It is generally accepted that good down (like most things, down has many quality levels) has the best weight-to-warmth ratio, which means you get the most warmth for the least amount of weight. Several disadvantages of down are the higher cost and the lack of insulating value when it become wet. Synthetic insulations, on the other hand, are more affordable, require less care and attention, and also come in several different types. Because most of our sleeping bags use synthetic insulation, we'll discuss them in more detail below.
The most popular synthetic insulations can basically be divided into 2 main categories - individual staple length fibers and continuous filament fibers. Because we use stable length fibers, we'll discuss them first.
We find it easiest to think about individual sleeping bag insulation fibers as being like pieces of hair. The term that is used to describe the diameter of these "hair like" fibers is called denier. The smaller the denier, the finer (smaller diameter) the insulation fiber will be. Our normal fibers are in the 7 to 9 denier range and our micro-fibers are in the range of 1.5 to 5. The smaller, finer denier fibers are more "down like", giving them a better weight-to-warmth ratio. They also tend to be a little bit more compressible, but like down, they also can be more expensive. Another advantage of synthetic stable length fibers is that it's very easy to mix fiber deniers, allowing us to find the best mix of price (larger denier) and performance (smaller denier).
Other factors that influence the performance of fibers are the "crimp", the fiber treatment, and the fiber construction. Back to our hair discussion, think of crimp as the amount of "curliness" a fiber has. Perfectly straight fibers would not be very "lofty", but when you add crimp to a fiber, it takes less of them to form a pile, naturally making them loftier. Now throw on a silicone type treatment, which allows the fiber to "recover" easier and faster after it's been compressed, and you're starting to get a fiber that is very thermally efficient. While it's difficult to imagine putting holes inside a hair-sized fiber, that's another thing fiber manufacturers can do to increase a fiber's warmth... add holes inside the fibers so more air can be trapped. So to re-cap, stable length fibers rely on the denier (diameter) of the individual fiber, the "mix" of the fibers (all larger denier, all smaller denier, or a mix of both large and small), the crimp (amount of curliness), finish (how slick the fiber is) and fiber construction (solid, one hole, multiple holes, etc.) to determine and maximize the thermally efficiency.
So here are a few more quick comments about micro-fiber insulations. The "magic" to them, as briefly mentioned above, is their ability to trap more air in the same amount of space/loft, because of their extremely small, fine size. These fibers were originally developed for the clothing/ski industry, because they're more interested in "less bulk for the same warmth"... you know, to eliminate the "Michelin-man look". Because backpackers and hikers are also interested in reducing weight and bulk, these micro-fiber insulations have made their way into sleeping bags.
The other synthetic fiber type is called "continuous filament". Rather than using individual staple length fibers to form the insulation batt, continuous filament fibers are just as the name suggests... a continuous piece of "hair-sized" synthetic fiber. The general advantage of continuous filament bags is their ability to be a little bit more "durable" when it comes to washing, long term "loft life", etc.... but we believe the advantages of staple length fiber bags (generally more compressible, usually feel softer, etc.) out-weigh the continuous filament bags, especially when you consider that proper care of staple length bags can offset the continuous filament.
As we've already mentioned, we mainly market sleeping bags with synthetic insulations, so we're going to focus on the construction methods we use for our synthetic bags. The main goals for the construction of any bag are to maximize the efficiency of the insulation and to eliminate (or greatly reduce) as many areas as possible that might have compressed insulation (like sewing lines). Keeping the insulation from shifting around is also very important, because if the insulation is allowed to shift (and not return), cold spots are formed. The 2 main construction methods we use are single layer, sewn through construction and multiple layer, offset construction.
- Single layer, sewn through - This is the method used in simple, basic rectangle bags, and exactly as the name suggests, there is only one layer of insulation, and it is held in place by sewing lines that are sewn through the outer and liner fabric. The biggest advantage of this method is that it's simple and inexpensive and the biggest disadvantage is that cold spots are created at each sewing line, making it not very thermally efficient.
- Multiple layer, offset construction - The way we like to simply describe this method is to call it a "bag within a bag". Most of the time we use 2 layers of insulation (for both the top and bottom of the bag). The individual layers are constructed like a single layer, sewn through bag. The cold spots are eliminated when the 2 layers are joined together at the edges, because the sewing lines are perfectly offset from each other. The sewing line from one layer is placed in the center of the sewing line from the other layer. In other words, the "thin spots" (sewing lines) are matched up with the "thick spots" (the area between the sewing lines), making for a nice, even blanket of insulation. For some specialty bags, we can use 3 layers on top and 2 layers on the bottom, and for some very cold weather bags, we can use 3 layers on the top and bottom of the bag.
We mainly use nylon and polyester fabrics for the shells of our mummy bags. We use taffeta (basic weave) and ripstop, which is a more specialized weave, that helps small tears and cuts from spreading. Like the insulation, which has its "diameter" measured by denier, individual fabric yarns are also measured in denier... and the smaller the denier, the more "silky and lightweight" the fabric is. Most of our mummy bag fabrics stay in the middle of the spectrum of denier... around 70 denier, which gives you the best blend of "soft and lightweight" and still strong and durable.
For our more rugged hunting bags, we use canvas fabrics that are either 100% cotton or a polyester cotton blend. These heavier fabrics offer much more strength, durability, and abrasion resistance, all characteristics that most hunters and fishermen are looking for.
As with the outer shell materials, liners also vary by the bag type, with mummy liners most often being different than rectangle liners. Our main mummy liners are nylon and polyester taffetas. One of our newer liner fabrics is a microfiber, and even though it's polyester, has the "warm and cozy feel" of cotton. For our hunting rectangle bags we like to use cotton flannel, because it's very soft and comfortable.
Sleeping bag shapes
We primarily use mummy shaped bags and rectangle bags... and a few of our rectangles have hoods, making them somewhat of a hybrid.
Because mummy bags are the most thermally efficient shape... and our best sellers... we offer quite a few options. Most other companies only have regular and long length bags, but we also have wides and extra-wides. Some people think our wide mummy bags are only for those campers that are larger, but we believe they are also in demand by campers that need the thermal efficiency of a mummy, but like the extra room of a rectangle. A wide or extra wide mummy gives them both... plenty of warmth and room to "move around".
Rectangle bags clearly give you more room inside to move around in, but that also means you have more room that needs to be kept warm, greatly reducing the thermal efficiency. Most rectangles also do not have a hood, so a bunch of your body heat escapes right out of the top of your bag. Rectangles with a hood can then offer you somewhat of a compromise... more room, but with a hood to keep some extra heat inside.