How to Choose a Sleeping Bag:Sleeping bags
come in a huge range of options, they are designed uniquely for different environments and intended uses, and vary significantly in price. When choosing a sleeping bag the first thing you need to decide is what you are going to be using it for. No sleeping bag will work in all conditions, so it is a matter of working out where you will use the bag, and what the temperature range will be when you are sleeping in it.
Camping Sleeping Bags:Camping
sleeping bags for easy access/car camping use are generally designed with comfort and value for money in mind. They are typically wider and longer than tramping or alpine sleeping bags, and can use either down or synthetic insulation. Camping
sleeping bags are, more often than not, designed for mild to warm climates and have relatively bulkier pack down sizes. This type of sleeping bag is perfect for car camping
, and travelling.
Tramping Sleeping Bags / Trekking Sleeping Bags:
Tramping sleeping bags are generally designed to minimize weight, while still maintaining a high warmth-to-weight ratio. To do this they are typically narrower in shape, and use high quality, high loft down insulation fill.
Alpine Sleeping Bags / Expedition Sleeping Bags:
Alpine sleeping bags are designed to be lightweight and provide excellent insulation in alpine environments. Alpine sleeping bags are narrow in shape to cut down on weight and to retain heat. Alpine bags are typically the most expensive type of sleeping bag due to the premium technology involved and the quality of materials used in construction.
Down vs. Synthetic Insulation:
Down is the natural plumage that forms the undercoating of waterfowl. It forms in tufts, or plumules, and consists of fluffy, wispy filaments. It is an exceptional insulator, prized for being light, easy to compress, durable and breathable. It excels in cold, dry conditions, or whenever weight and space-saving are priorities.
Down is more expensive than synthetic fill, but it maintains its loft (which provides its heat-trapping ability) at a near-original state longer than synthetics. That makes down a good value over the long haul. However, in damp or wet conditions, synthetic
fill (usually a type of polyester) is far superior than down. When down becomes wet or damp, it's ability to trap air and retain heat is significantly reduced. In comparison, synthetic fill is far less impacted by moisture. Synthetic bags
can also be dried much quicker than down bags
, are easier to clean, and are less expensive than down. However, synthetic is also bulkier, heavier and may have a shorter user life.
Duck Down vs. Goose Down:
Down comes from geese and ducks. Duck down has recently gained broad acceptance for use in outdoor products due to 1) advances in down processing techniques and 2) the scarcity of goose down, which has significantly driven up its price.All down, duck or goose, is measured according to fill power. Its ability to loft, and thus trap heat, is calculated by how many cubic inches that 1 oz. of down can fill in a testing device. Higher-grade down, taken from more mature birds, requires fewer plumules to fill space and achieve a certain temperature rating. So any bag rated +2°C with 700-fill-power down, no matter if its fill is duck or goose down, will be lighter than a +2°C bag using 600-fill-power down.
Yet place a pair of 600-fill-power sleeping bags side by side—one using duck down and one using goose down—and their loft, weight and compressibility will have little or no variance. Fill power is fill power. Here is where duck and goose down can potentially differ:
Top-end fill power (Loft): The most mature duck down can achieve fill-power ratings no higher than 750 or 800. Premium goose down can reach 900 and potentially even higher ratings, but it’s quite expensive. Super-light sleeping bags with fill power at 800 and higher will continue to be made with goose down. Expect high price tags.
Durability: Goose plumules are typically larger than the plumes of duck down and can potentially retain their lofting ability for a longer time. One manufacturer estimates the average lifespan of a goose down bag (at its original temperature rating) is 25 years, 20 years for a duck down bag.
Many major bag-makers have made the transition to duck down throughout their product lines. Quality testing and EN temperature rating standards are applied to duck down and goose down products alike, and performance standards should be the same.
What Are Sleeping Bag Baffles?
Baffle structure is crucial to the performance of sleeping bags, without it even the best quality down will not loft and insulate to its full potential and may clump, forming cold spots in areas where there is less down. Sleeping bag manufacturers use a range of different baffle structures in sleeping bags, each with different profile shapes and heights, and each carefully selected according to the bags end-use and overall fill-weight.
Furthermore companies have carefully tailored the material these baffle walls are constructed from. Helping to give a bag vital structure, allow airflow to circulate and prevent down migrating from one baffle to another, this hidden element of a bag's make-up can be critical to both its short and long-term performance. With quality baffle construction and after many years of hard use, the down in your sleeping bag will still be where it is intended to be, supported in exactly the right place.
Box Wall Baffles:
This is the simplest method of baffle construction and traps Down into parallel chambers, keeping weight to a minimum while allowing the Down to loft to its full potential. Being the easiest baffle to produce, it is also the cheapest but can also lead to the development of cold spots along the seams as the Down moves away from the baffle walls. Due to this, several other baffle methods were developed.
Slant Wall Baffles:
Another simple baffle method, slanting the baffle walls along an axis means that even though the Down may shift inside the baffle, it is less likely to develop cold spots as some Down will still be covering that area of the baffle. The Down is still able to loft well inside the open baffle tube, increasing thermal efficiency and stability but due to the smaller area close to the corners of the baffle zone, small ‘cool’ spots can still develop.
By alternating the size of the top and
bottom baffle zones, Down is able to loft to its maximum but where the Down is
more likely to clump together or leave un-insulated, the opposing baffle zone
will cover. Trapezoid baffles minimize the development of cold spots and
increase thermal efficiency but at the expense of extra weight and less
compressibility in comparison to their alternatives.
Offering the largest degree of seam overlap, this method of construction provides the greatest thermal insulation and the strongest baffle stability at the expense of slightly extra weight. This type of baffle is used in sleeping bags where only best insulation is required.
Draft tubes / Zip baffles:
Draft tubes are a common feature in sleeping bags where warmth is paramount in their design; these baffles line the length of the zipper to avoid cold spots developing where there would otherwise be no insulation. In sleeping bags made for very cold environments there is often a double baffle – one on either side of the zip which vastly reduces the amount of cold air able to pass through into the bag, and warm air able to escape. Often these draft tubes will also connect to a neck baffle, the purpose of which is two-fold; to trap the warm air from your torso inside the bag and also to stop cooler air coming in through the open area around your face. The draft tubes and neck baffles can be filled with either down, synthetic or a mixture of both depending on the requirements of the sleeping bag and the weight, bulk and stability required of the baffle’s fill.
The overall purpose of the hood is to protect the neck and head while also providing maximum warmth retention from the main body of the bag. In order to prevent heat loss, the hood must have a baffle construction which allows the fill to loft to its full potential while also minimizing fill migration and the development of cold spots. To maximize warmth the hood must also be anatomically shaped to for thermal efficiency. As the required warmth of the sleeping bag increases the required control of the fill must also increase; more baffles and altered baffle orientation increase the control and stability of the down, increasing insulation and ultimately comfort in the more extreme environments.
A sleeping bag foot box is designed in a similar manner to the hood; it needs to protect and insulate the feet, minimize heat loss through the end of the bag and also maximize comfort. The overall shape and design of the foot box will depend largely on the intended purpose of the sleeping bag. Comfort and travel oriented sleeping bags will have a wider toe box for more foot room which will often zip right through and have little or no baffle structure. As the requirement for additional warmth and insulation increases, the toe box’ internal room will shrink and become baffled and more anatomically shaped. Often the toe box becomes angled to allow the foot to rest in a more natural position for comfort and with no detriment to warmth. The baffling of the toe box serves the same purpose as with the hood; to control the fill, minimize fill migration, reduce cold spots and allow maximum lofting, therefore providing as much insulation as possible. Sleeping bags aimed at maximum insulation will not zip out through the toe box because this would create an unnecessary cold spot, reduce compression and likely add weight.
With no extra increase in weight, using elastic material in the lining of the fabric pulls the fabric away from the down, allowing it to loft to its full effect while also minimizing ‘dead space’ in the sleeping bag. In order for a sleeping bag to have maximum warmth for its fill it should have minimal loose, empty space inside. Elasticized baffles are primarily designed to squeeze out the empty space so that your body warms the inside of the bag more efficiently and less cold air is able to form. Tests have shown that elasticated baffles are able to increase the warmth of the bag by up to 2°C. While sounding insignificant, this can be the difference between having a good night’s sleep and suffering hypothermia when you are pushing the limits of your sleeping bag’s performance.
Sleeping bags will use a combination of the previous designs to maximize the core requirements of the bag, ultimately making them better for their intended use. As an example, alpine sleeping bags will often orientate the torso baffles longitudinally rather than horizontally. The purpose of this is to minimize the fill migration from the torso zone, as gravity will cause the fill to move to the lowest area of the baffle. In this case, the fill cannot move off the torso due to the longitudinal baffles and the warmth of the sleeping bag will be maintained over a longer period, extending its life in harsh environments.
In addition to the fill, loft, baffle type, elasticity, hood and foot piece, the overall shape and length of the sleeping bag also plays a key role in its warmth in any environment and is designed around an intended use. Expedition sleeping bags will usually have MORE room inside than alpine bags, because they are designed to have room for additional gear inside the bag which will increase its warmth. Alpine bags will be a very snug fit and taper sharply from the shoulders through to the feet in order to maximize thermal efficiency and minimize carrying weight. A mountain/comfort fit is designed with more comfort in mind and has additional leg room and less taper from the shoulders since warmth is not necessarily the main purpose for the bag. A women’s specific fit is often an option additional to other fit types and is a shorter overall length, deeper foot baffles and less taper from the shoulders due to a ladies wider hips, but a larger taper from the hips to the feet.