Wool and merino wool are excellent insulating fabrics (Figure 93-2, online). The core of the wool fiber absorbs moisture and redistributes it to the fabric surface, where evaporation occurs. This moderate affinity for absorbing moisture is countered by excellent regain—the fabric retains warmth and does not feel cool or wet when damp. Wool feels wet when saturated. Traditional wool can be highly irritating to the skin. Wool fibers have barbs in the epicuticle, or outer layer of the fiber. Merino wool is a finer fiber with fewer barbs in the epicuticle. Ultrafine merino wool fibers are 17.5 µm in diameter, allowing for lightweight fabrics and exceptionally tight weaves. (For comparison, a human hair is 60 µm in diameter.) Merino wool is machine washable with minimal shrinkage and is highly elastic. It retains its shape well with repeated wearing and washing. The antibacterial properties of wool contribute to decreased body odor retention—a very desirable quality when faced with multiple days of wear. The bacteria that metabolize sweat do not flourish; therefore less odor-producing metabolites are present.

FIGURE 93-2 Icelandic sheep.

Wool, including merino wool, is spun from the fleece of sheep. Alpaca and llamas are camelids, originally from South America (Figure 93-3). Cashmere is spun from the undercoats of cashmere goats. Although technically not wool, these wool-like fibers share similar properties with Merino wool.

FIGURE 93-3 A, Peruvian llama overlooking Machu Picchu. B, Peruvian llama.

Silk is used most commonly in base layers. Conventional, untreated silk retains moisture, although not to the degree of cotton. The majority of silk used for outdoor clothing is treated and wicks reasonably well. Silk is frequently blended with other fibers to smooth the texture of the fabric.

Down

Down is the fluffy undercoating that keeps geese, ducks, and other waterfowl warm (Figure 93-4). It consists of clusters of filaments growing from a central quill point. Land fowl do not produce down. Goose down is superior to duck down in its loft and therefore ability to insulate. Down is an excellent insulator when dry. Unfortunately, the low moisture regain and hydrophilic nature of down make it almost useless when wet. The insulative value of down is measured in fill power. Each company uses a slightly different measurement, making across-the-board comparisons difficult. Generally, the higher the fill power, the greater the insulative value. Fill power is the volume that a specific weight of down occupies. In other words, the number of cubic inches displaced by a given ounce of down (in³/oz) is the fill power.

FIGURE 93-4 Down puff.

The highest-quality down has a fill power of 800 or greater and is usually goose down. Lower-quality products use duck down. A 600–fill power garment may be as warm as an 800–fill power garment, but more down is needed to achieve the same warmth, thus the garment will be heavier. Down is the preferred insulation in cold, dry environments when rain is highly unlikely.

Fur, Leather, and Hides

Historically, protective clothing was made from animal products. Hides, feathers, and even intestines have been used to make garments. Northern indigenous peoples continue to use fur and pelts for outerwear. Pelts and hides are water resistant, warm, and physically protective. However, they are heavy and may be considered cumbersome. They demonstrate little flexibility or stretch. Fur trim may still be used around hoods and the sleeve cuffs but has largely been replaced with wool fleece or synthetic fibers. These trims trap air, which stagnates and warms, forming an insulating area around the face and wrists.

Leather is the finished product of tanned hides. It may be made from any animal, with cow, goat, and sheep being the most common. Leather, depending on the finishing process, can be exceptionally soft, supple, and thin, or it can be tough, thick, and abrasion resistant. Leather is commonly used in the manufacture of footwear and gloves, capitalizing on its durability. However, synthetics have replaced leather in most outdoor clothing. Abrasion-resistant nylon is now used on the cuffs, shoulders, and elbows, where leather may have been used in the past. Leather jackets and pants are still very common for motorcycle gear, and thick leather pants or chaps are still used by woodsmen. Leather is not water resistant and becomes readily saturated unless treated with agents such as mink oil, Sno-Seal, or other oil-based products.

Synthetic Fibers

Polyester is the general term for any petroleum-based fiber. It is widely used in the outdoor industry and highly versatile. Fibers are extruded or formed, not spun as are natural fibers. The fibers can be formed into nearly any thickness or configuration. Polyester fabrics insulate well because the fibers do not conduct heat efficiently. The fibers do not actually absorb any moisture. The moisture travels along the surface of the fiber and out to the surface of the fabric. Polyester fabric dries very quickly. These properties are used to their full advantage when polyester is made into fleece and sheets of insulation. Fleece is soft, washable, and durable. Bulky fleece traps air and is exceptionally warm for its weight. When fleece is tightly woven, wind and water resistance improve, but insulative value is diminished.

Polyester that is formed into sheets of insulation may be sewn into the layers of a garment. Polyester insulation has high moisture regain and good evaporative qualities; however, it is not as light or compressible as down. The fibers may deteriorate and break down with repeated use and washing and thereby lose the insulative value. Both down and synthetic insulations must be stored noncompressed. Prolonged compression damages both down and synthetic fibers, causing loss of loft and insulation.

Polypropylene was one of the first synthetic fabrics used for base layers. It wicks moisture well, has low thermal conductance, and is durable. Unfortunately, it demonstrates high odor retention and stains very easily. Other polyester fabrics, such as Capilene, Polartec, Coolmax, and REI MTS, have largely replaced it.

Nylon, like polyester, absorbs little water, which permits rapid evaporation. It has high moisture regain, is highly abrasion resistant, and melts easily. Nylon can be formed into large-diameter fibers and woven into highly durable fabrics, which are frequently used to reinforce wear points. Nylon must be tightly woven to protect against wind and water. This comes at the expense of breathability.

Blends

Manufacturers blend fiber types to use the benefits of each fabric. For example, spandex may be blended with the primary fiber, such as wool or cotton, to improve stretch and retention of shape. Wool may be blended with polyester to improve durability and fit (Tables 93-1 and 93-2).

TABLE 93-1 Comparison of Synthetic Fabric, Wool, and Silk

TABLE 93-2 Comparison of Down with Synthetic

	Down	Synthetic
Compressibility	Excellent	Good
Insulative quality when wet	Poor	Good
Weight	Lighter per volume	Heavier than down
Durability	Will last longer if cared for properly	Will eventually break down even with ideal care
Care	Requires careful laundering	No special product required
Warmth	Greater warmth-to-weight ratio
Allergenic properties	Possible	None
Expense	High	Moderate
Drying time	Slow	Fast

Waterproof/Breathable Fabrics

Waterproof/breathable fabrics are designed to repel precipitation and allow perspiration, in the form of water vapor, to escape. These actions help to regulate body heat by keeping clothing dry and preventing perspiration from accumulating within the clothing during exertion in rainy environments. Fabrics are made waterproof/breathable through the application of laminates, coatings, and durable water-repellent (DWR) finishes.

Laminates

Laminate fabrics are designed by bonding a waterproof/breathable membrane to the underside of the garment’s exterior. They are commonly bound to nylon. If there are only two layers, the fabric is designated “two-ply.” The laminate may be sandwiched between two layers, thus creating a three-ply material, which is more durable but heavier than two ply. W. L. Gore and Associates produced the first waterproof/breathable membrane—Gore-Tex. This trade name is commonly, and incorrectly, used to refer to the entire category of laminate clothing (Figure 93-5). Although many manufacturers and laminate types now exist, the basis of laminate technology is the membrane. The membrane is formed of stretched or expanded polytetrafluoroethylene (ePTFE). The process of expanding the PTFE introduces microtears or holes in the laminate. These openings are small enough to allow water vapor of perspiration to escape (breathability), while not allowing water droplets to enter from the environment (water resistance). The pores of the ePTFE are 20,000 times smaller than the smallest raindrop, yet large enough to allow water vapor to pass to the outside. Water can only penetrate ePTFE if it is applied with a great deal of force or if the surface of the ePTFE is contaminated or soiled, leading to leakage. Two of the predominant manufacturers, Gore and eVent, use different methods to address soilage. Gore applies a microthin layer of polyurethane to the laminate. It is designed to be porous and not affect breathability of the fabric. eVent uses a proprietary method employing integration of a substance into the laminate itself. By preventing soilage, the waterproof and breathable properties of the fabric are sustained.

FIGURE 93-5 Arc’teryx Alpha LT hard-shell jacket is a lightweight and fully waterproof jacket with the harness HemLock feature, ideal for use with a climbing harness. A light, three-layer Gore-Tex shell.

(From http://www.arcteryx.com.)

Coated Fabrics

Coatings are liquid solutions, predominately polyurethane, that are applied to the interior of the garment. Microporous coatings are formed of microscopic channels that are too small for droplets to penetrate yet porous enough to allow vapor to escape. These channels form as the coating adheres to the surface of the fabric, either secondary to foaming agents that form interconnected pores or to introduced solids that cause microscopic cracks in the coating. Monolithic coating agents form a hydrophilic layer that transports moisture to the surface. Microporous and monolithic coating methods are virtually indistinguishable. Some manufacturers use both methods. Coated fabrics are not as breathable as laminates and are generally not as durable. However, they are more compressible and significantly less expensive than laminate fabrics.

Rubberized nylon is coated with a robust polyurethane lining that is not breathable but is waterproof. This fabric is ideal for marine environments and sedentary activities, when sweat accumulation is less of an issue for temperature control.

Soft-Shell Fabrics

Soft-shell fabrics are the most newly developed fabrics in the outdoor clothing industry. This fabric type excels in breathability and flexibility yet still demonstrates moderate water resistance. Soft-shell fabrics have a tightly woven outer layer and an inner lining of varying insulative quality and may additionally employ a windproof or highly water-resistant laminate (Figure 93-6, online). They combine the properties of both an insulating middle layer with a protective outer layer. Soft-shell garments are highly effective for both temperature and moisture management in environments where rain is unlikely. They are moderately water resistant due to the tightly woven exterior surface and DWR finish. These garments excel when used during highly aerobic activities and in conditions where rain is not a concern. Soft-shell garments may function as both an insulating (middle) and outer (protective) layer.

FIGURE 93-6 The Arc’teryx Gamma AR jacket is a highly breathable, insulated, soft-shell jacket with anatomic shaping for maximum mobility.

(From http://www.arcteryx.com.)

Durable Water-Repellent Finish

A DWR finish is applied to all waterproof/breathable fabrics after the garment is completed. It does not change breathability of the fabric but enhances water resistance by causing water to bead up and roll off the garment’s exterior. The finish bonds to the fibers and does not fill the interstitial spaces of the fabric. An ideal DWR finish forms a dense chemical buffer on the outer surface of the garment. Microscopically, the finish forms an upright, spiky, and brush-like texture. Water thereby has a high contact angle with the finish, forming a spherical droplet. Were the contact angle to be low, water droplets would flatten into a more dome-like shape. This would allow the water to cling to the surface of the fabric and eventually seep in (Figure 93-7).

FIGURE 93-7 Watertight zipper and fabric with durable water-repellent finish.

Layering

Dressing in layers enhances one’s ability to adapt to a changing environment. Each layer should maximize the properties of the fabric from which it is made. Layering allows for addition and subtraction of clothing as needed, adjusting for changes in body temperature and metabolic output, resulting in more efficient maximization of metabolic heat and enhancement of energy conservation. Adjustment of layers in response to changes in the environmental or travel conditions can prevent sweating and overheating, while preventing loss of heat that might lead to undesired cooling. In anticipation of increased body heat and sweating when traveling uphill, layers can be preemptively removed and zippers unzipped to enhance ventilation. Clothing that becomes saturated in sweat is not only uncomfortable, but loses its insulative properties as the fibers become soaked with moisture. This is clearly important in a cold environment, where loss of insulation or long drying times may lead to hypothermia. Removing layers in response to increased work also serves to conserve energy and moisture. In contrast to removing layers to prevent sweating, adding clothing layers as the workload decreases or the environment cools allows heat to be trapped in the insulative layers. The simple actions of managing a personal layering system conserve valuable energy for outdoor endeavors (Figure 93-8, online).

FIGURE 93-8 Sarah Hueniken keeping warm layered up in Outdoor Research clothing between climbs.

An efficient layering system allows rapid response to changing environmental conditions. It is easier to replace a single garment that has become soiled or saturated than to replace an entire suit of clothing. Through layering, it becomes possible to not only pack fewer garments, but still be more comfortable across a wider range of environmental conditions and activity levels. When packing for any wilderness excursion, the unexpected needs to be considered, such as precipitation in the form of rain or snow, a sudden change in temperature, or the unexpected night out. When dressing in layers, fit is very important. The base layer should be snug but not confining. The middle layer should fit over the base layer comfortably. The outer layer needs to be large enough to fit over both base and middle layers without compressing. Compressing the middle layer reduces its insulative properties. Harness or pack straps should not rub or chafe on any seam or fold of fabric. Testing the fit, comfort, and effectiveness of the layering system before venturing into the wilderness will help prevent not only the discomfort of poor-fitting layers, but ensure that the purpose of the layering system is fulfilled—keeping one warm and conserving energy (Box 93-2).

BOX 93-2 Insulating Value of Clothing

The insulating value of clothing is measured in clo. Clo was first defined in 1941 as a more descriptive measure of thermal resistance for clothing. One clo is the amount of clothing necessary for a sedentary person to be comfortable in an environment with an ambient temperature of 21.1° C (70° F), a relative humidity of less than 50%, and normal ventilation (air movement measured at about 0.5 mph). A lightweight business suit has an approximate clo value of 1.0. The lowest clo value is 0.0 and is that of a naked individual. The highest practical clo value (4) is that of Eskimo fur clothing. Today’s manufacturers rarely use clo as a comparative unit. Polartec grades its fleece by 50, 100, 200, and 300; other manufacturers grade garments by light, mid, and heavy weight. Comparing garment type is more practical for most users. What follows are some generalities about different layer types.

	Approximate clo Range	Garment Example
Base	0.15-0.3	Silk weight, cotton T-shirt
Lightweight	0.30-0.50	Polartec 100, Patagonia R1
Midweight	0.75-0.85	Polartec 200, MontBell Thermawrap parka
Heavyweight	0.90-0.11	Polartec 300, Patagonia Polarguard Delta pullover
Expedition	1.40 and greater	Patagonia down pullover and most high-loft insulation