Layered clothing

Layered clothing is a manner of dressing using multiple garments that are worn on top of each other. Some of the layers have different, largely non-overlapping, functions. Using more or fewer layers, or replacing one layer but not others, allows for flexible clothing to match the needs of each situation. Two thin layers can be warmer yet lighter than one thick layer, because the air trapped between layers is a good insulator.

Layered clothing is particularly relevant in cold climates, where clothing must at the same time transfer moisture, provide warmth, and protect from wind and rain. In a hot and dry climate, clothes have very different functional requirements: they must block the radiation from the Sun, and allow for sufficient air circulation. Therefore, layered clothing in the sense used in this article is largely irrelevant to hot and dry climates.

Outdoor and sports wear manufacturers favor layered clothing because, among other reasons, it allows them to offer so-called "technical" or "functional" clothes which are optimized for the particular demands of a specific layer. Such clothes are often made of advanced synthetic materials, and can be expensive.

Layers

Usually at least three layers are identified as follows:

* Inner layer provides comfort by keeping the skin dry. Also called "base layer".
* Mid layer provides warmth. Also called "insulating layer".
* Shell layer protects from wind and water. Also called "outer layer".

Often clothes combine two adjacent layers, as in the case of warm undergarments that provide both comfort and insulation.

Inner layer

The purpose of the inner layer is to draw the sweat away from the skin to the next layers, which makes the wearer feel warmer and more comfortable. The transfer of moisture happens due to capillary action. This is sometimes called wicking, and thus the used materials are called "wicking materials". When moisture has moved from the skin into (nonabsorbent) clothing, it has more surface area and will evaporate faster. If a piece of clothing does not transfer moisture well, it is not strictly an inner layer garment at all, but simply a comfortable mid-layer garment.

* Synthetic materials such as polyester and microfiber-based fabrics are good choices as they do not absorb moisture but may transfer it well. On the other hand they can be expensive.

* Silk feels more comfortable, but is weaker and harder to take care of, and is less commonly used.

* Cotton is cheap and feels comfortable when dry but absorbs moisture easily and is slow to dry out, especially in cold conditions. Cotton is better suited for the middle layer.

Mid layer

The mid layer is needed in cold weather to provide additional insulation. For maximum warmth, multiple thin mid layers can work better than one thicker layer. The use of multiple thin layers also facilitates adjustment of warmth. The mid layer should be more loose-fitting than the inner layer, as this leaves insulating air between the layers. However, if best possible moisture transfer is desired, too great a gap between any adjacent layers of clothing may reduce the moisture transfer by capillary action from one piece of clothing to another. On the other hand, very loose-fitting layers can allow more removal of moisture (and heat) via air circulation.

* Wool is the traditional mid layer material with several good properties: it has good insulation even when wet, absorbs moisture but does not feel wet even when it holds significant moisture, and transfers moisture.

* Fleece made from PETE or other synthetics has many of the features of wool, but is lighter. It provides good insulation even when wet, absorbs very little moisture, and dries quickly. Although no longer commonly used in the industrialized world, natural sheepskin fleece could also serve the mid layer function.

* Down has a very good warmth:weight ratio, and can be packed down (squeezed) to take very little room. On the downside, it is expensive, makes a thick garment, dries slowly, loses its insulating properties when wet or compressed, and stops lofting properly after being washed several times.

* Synthetic Fiberfill such as polyester fiber is used similarly to down, but does not have as good a warmth:weight ratio. However, it is less expensive, provides good insulation even when wet, dries quickly, and absorbs very little moisture. Thinsulate is a brand of very fine fiberfill that provides higher warmth for a given thickness.

* Cotton, as with the inner layer, is a cheap alternative, but a reasonable choice only when low insulation and moisture transfer is needed.

Shell layer

The outermost clothes are called the shell layer, but only if they block wind or water, or have good mechanical strength. If wearing, for example, just an undershirt (inner layer) and a fleece jacket (mid layer), there is no shell layer. Ideally the shell layer lets moisture through to the outside (that is, is breathable), while not letting wind and water pass through from the outside to the inside. While this is enabled to some degree by modern materials, even the best and most expensive materials involve a trade-off between breathability and water- and wind resistance.

If heavy sweating is expected, one should avoid wearing any shell layer garments unless their protective properties are essential. For example, when one is jogging, no shell layer is likely to be able to transfer enough moisture to keep the wearer feeling dry. Instead, one should consider using sufficiently warm mid layer clothes.

* Plastic raincoats protect completely from water and wind, but let through no moisture. To compensate for that, such raincoats usually have flap-covered holes and are very loose-fitting at the bottom to allow air circulation.

* Waterproof breathable (hard shell) materials are waterproof and somewhat breathable. Their essential element is a thin, porous membrane that blocks liquid water, but lets through water vapor (evaporated sweat). The more expensive materials are typically more breathable. The best-known brand is Gore-Tex.

* Water resistant (soft shell) materials block water only partially. On the other hand they are usually more breathable and comfortable, thinner, and cheaper than completely waterproof materials. Water-repellent coatings are often used. Before waterproof-breathable shells were invented, the "60/40" (60% cotton, 40% nylon) parka was widely used. While the soft-shell approach has never actually gone away ( [http://www.buffalosystems.co.uk/ UK company Buffalo] making its pile-lined Pertex shelled garments since the 70s, for example) it has expanded greatly in recent years, with the term "soft shell" itself being created with the recent upsurge in interest and use. Soft shell fabrics come in numerous varieties with many garments combining different fabrics. In many cases these garments include insulation, aiming to replace several layers with a single highly flexible one.

Adjusting a layering system

It is not always necessary to wear all layers, and the choice of how many to wear and what garments to use depends very much on the activity and the weather conditions likely to be encountered, and that more layers and insulation are not necessarily better. In fact, trapped dry air is the main insulator in clothing, and as long as the wind is effectively managed, a few millimetres of fabric often suffice to provide insulation.

On the other hand, sweat build up inside layers can be deadly, even if the fabrics worn maintain their insulating properties while wet rapid cooling can still result by the energy being leached from the body by the evaporation of trapped moisture, leading to the onset of hypothermia. Thus it is critical to adjust layers to maintain sweat transport during periods of heavy exertion and to avoid overheating and the accumulation of moisture inside the layering system. Keeping an over-warm sweater or fleece on during a period of heavy exertion can lead directly to hypothermia later when trapped sweat re-condenses. [http://www.psychovertical.com/?theartofnotsuffering]

Alternatives to layering for outdoor clothing

Conventional layering does have its disadvantages for outdoor clothing - in particular it can be crucial to adjust the amount of insulation worn to respond to conditions, but this can only be done by removing the outer shell layer. This can expose the insulating layers to rain, or be inconvenient or even dangerous to perform while rock climbing or adventure racing. Radical alternatives to layering seek to reduce the need to remove layers to adjust body temperature, and to improve the removal of sweat through having a single garment (possibly worn over a wicking baselayer) which provides warmth, wind proofing and possibly water proofing.

A typical design is a smock that allows sweat transport and body temperature to be adjusted through a series of vents at the neck and the armpit, made of a fabric that wicks sweat away from the skin. These systems can either be "warm while wet", by-passing the normal need for a waterproof layer in most conditions, or themselves be waterproof bust still breathable. Montane and Buffalo "pile and pertex" clothing are perhaps the most famous examples of the first type, while Paramo are of the second, fully waterproof variety, with the Paramo Velez smock made Nikwax Analogy fabric corresponding closely to the design discussed. [http://www.psychovertical.com/?thebestsoftshell] [http://alexwade.com/articles/20021027_good_gear.html]

Fashion use

Combining different garments in layers can be used to create a variety of outfits. This provides similar practical benefits to practical layering, in that the wearer can shed layers according to changes in temperature, and is also a way of making use of clothing to produce different looks and mix colours in various ways.

ee also

* Waterproof fabric
* Durable Water Repellent
* Heated clothing

External links

* [http://www.psychovertical.com/?theartofnotsuffering A scientific approach to layering for hikers and mountaineers]
* [http://www.basspro.com/servlet/catalog.CFPage?mode=article&objectID=29900 Learning to Layer Clothing]
* [http://haglofs.se/tip/dress_right.asp?lang=en Haglöfs clothing page]
* [http://www.abc-of-hiking.com/hiking-apparel/three-layer-system.asp ABC of Hiking]