The hydrophobic or hydrophilic nature is accomplished either by the physical characteristic of the fabric itself or by applying a chemical coating to the fabric. Examples: Capilene, Lifa, and Dryline.
Micro-channel Fibers These are synthetic fibers with tiny channels or capillaries within the individual fabric threads. These fabrics rely on what is known as “capillary action” to transport moisture through the channels from next to your skin to the outside of the fabric. Some fabrics are bicomponent with an inner layer of macrofiber yarn and an outer layer of microfiber yarn. The outer layer has a much greater surface area, which helps “pull” the water to the outside of the fabric. Examples: CoolMax and Polartec PowerDry.
Some of these fabrics have a definite “inside” and “outside.” If you wear a bicomponent garment inside out, you defeat the purpose of the garment. Garments that rely on the physical characteristics of the fabric itself rather than a chemical coating continue to function regardless of the number of times they are washed, while those that rely on a chemical treatment may eventually “wear out.” There are different thicknesses of these fabrics, generically called lightweight, medium weight, and heavy or expedition weight. The thicker fabrics offer great insulative value along with their wicking properties. Pro: Excellent inner layer. Minimizes moisture next to the body, where high conductive heat loss can occur. Con: Not windproof, so best used as an inner layer. Some fabrics retain odor more than others.
The Insulating Layers
The main purpose of the insulating layer is to create dead air space for insulation. It also absorbs some of the wicking layer’s moisture, keeping the moisture away from your skin, so you want it to easily pass moisture. Depending on the temperature this can be one layer or many layers.
First Layer Your first insulating layer is typically shirts and pants. This could be an extension of the wicking layer—for example, wearing middle-weight to expedition-weight polypropylene that both wicks and provides insulation. Layers that allow you to “open” and “close,” like zip-front turtlenecks or button-down shirts, allow for ventilation during periods of high heat-producing activity. Synthetics like polypropylene or Thermax work well in this layer.
Second Layer If you need more loft for insulation, add another insulating layer like synthetic fleece or wool pullovers, sweaters, jackets, and pants.
Outer Layer If it is really cold, you may need to add an even thicker layer like an insulated parka or pants. These typically have an outer and inner layer of fabric and either down or some synthetic insulating fill sandwiched in between. These layers are often worn at the beginning and end of the day in camp, when activity levels are low or in temperatures below freezing.
The Insulating Materials
Fleece is a synthetic fabric often made of a plastic (polyester, polyolefin, polypropylene). It has a “fuzzy” 3-D quality that imitates a sheep’s fleece and gives it insulating properties. It remains warm when wet, does not absorb moisture, and dries very quickly. This material has an insulative capacity similar to that of wool. Fleece is manufactured in a variety of thicknesses, offering different amounts of loft and insulation and numerous layering possibilities. Some fleece garments are made from recycled plastics or with a middle wind-proof layer. Pro: Fleece is able to provide the equivalent warmth of wool at half the weight. Con: Fleece by itself has poor wind resistance and almost always requires an additional wind-resistant layer. Examples: Polartec 100, Polartec 200.
TRICKS OF THE TRAIL
Loose fill versus continuous fill Insulating fibers can either be loose fill, like down, or continuous fill, like Polarguard. Loose fills are made up of small individual fibers. In order to keep the fibers equally distributed throughout the sleeping bag or garment, the manufacturer has to sew in interior “walls” of fabric known as baffles to create individual compartments to hold the fill. This adds a lot to the manufacturing cost.
Continuous-fill fibers are made in large sheets that can be cut into the right shape and sewn directly into the sleeping bag or garment without baffles.
Wool derives its insulating quality from the elastic, three-dimensional wavy crimp in the fiber that traps air. Depending on the texture and thickness of the fabric, as much as 80 percent of wool cloth can be air. Wool can absorb a fair amount of moisture without imparting a damp feeling because the water “disappears” into the fiber spaces. Even with water in the fabric, wool retains some dead air space and will still insulate you. The disadvantage to wool is that it can absorb a lot of water, making it very heavy when wet. Maximum absorption can be as much as one-third the garment weight. Wool releases moisture slowly, with minimum chilling effect. Pro: Tightly woven wool is quite wind resistant. Wool clothing can often be purchased cheaply. Con: Wool garments can be heavy, take a long time to dry, and can be itchy against the skin. Some people are allergic.
Down The very soft underbody plumage of geese or ducks provides excellent insulation and dead air space for very little weight. (Goose down is finer quality than duck.) Down is rated by its fill power, or how many cubic inches of volume an ounce of down will fill. Fill power goes from 550 cubic inches up to 800—a 700-fill sleeping bag lofts better and is more thermally efficient than a 550-fill bag. Most high-end sleeping bags are made of 700 fill; 800 fill is mostly for expedition-quality garments and sleeping bags.
Since down is a loose fill, sleeping bags and clothing must have a series of small compartments sewn in with baffles to hold the fill evenly throughout, which adds to the manufacturing cost. Down is useful in sleeping bags since it tends to conform to the shape of the occupant and minimizes convection areas. It is also very compressible, which is an advantage when packing. But the same compressibility means that your body weight compresses the down beneath you, significantly reducing your insulation from the cold ground, so you need an insulating pad underneath you more so than with a synthetic bag. Pro: Excellent insulator. Incredible warmth-to-weight ratio. Compresses to extremely compact size. Long life span if cared for properly (up to 20 years). Con: When down gets wet it simply clumps together and loses almost all of its insulative value and is almost impossible to dry in the field. Use depends on your ability to keep it dry. When using a down sleeping bag, take special care to prevent it from getting wet. For example, a vapor barrier sleeping bag liner in a down bag will help the bag stay dry from the inside and a waterproof-breathable bivy sack will help the outside keep dry. Keeping the bag in a waterproof stuff sack will protect it during the day. In wet conditions a down-fill outer parka may get soaked, and a synthetic-fill would be better. Down is a loose fiber fill that requires baffles (see “Tricks of the Trail,”.) Expensive. Some people are allergic.
Synthetic Fibers There is a multitude of different synthetic fibers used for garment and sleeping bag fills. Most are based on some form of polyester. These are primarily used in sleeping bags and heavy outer garments, like parkas. The fibers are fairly efficient at providing dead air space (though not nearly as efficient as down). Some products like Polarguard are made in large sheets. Others create additional dead air space by having hollow channels within the fiber (e.g., Quallofil). Pro: They do not absorb water and dry fairly quickly. Some fibers are produced in sheets that do not require baffling. Con: Heavy. Not as efficient an insulator as down. Hard to compress to a small size. Some are loose fibers that require baffling. Fibers produced in sheets tend to break down over time, losing their loft more quickly. Examples: Polarguard 3D, Polarguard Delta, Quallofil.
“Superthin” Fibers These synthetic fibers are
