Thermal Insulation and Clothing
The term thermal insulation can refer either to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. Heat energy can be transferred by conduction, convection, radiation. Thermal insulation prevents heat from escaping a container or from entering a container. In other words, thermal insulation can keep an enclosed area such as a building warm, or it can keep the inside of a container cold. Insulators are used to minimize that transfer of heat energy. In home insulation, the R-value is an indication of how well a material insulates. The flow of heat can be reduced by addressing one or more of the three mechanisms of heat transfer and is dependent on the physical properties of the material employed to do this.
Clothing is chosen to maintain the temperature of the human body.
To offset high ambient heat, clothing must enable sweat to evaporate (cooling by evaporation). When we anticipate high temperatures and physical exertion, the billowing of fabric during movement creates air currents that increase evaporation and cooling. A layer of fabric insulates slightly and keeps skin temperatures cooler than otherwise.
One of the primary purposes of clothing is to keep the wearer comfortable. In hot climates, clothing provides protection from sunburn or wind damage, while in cold climates its thermal insulation properties are generally more important. Shelter usually reduces the functional need for clothing. For example, coats, hats, gloves, shoes, socks, and other superficial layers are normally removed when entering a warm home, particularly if one is residing or sleeping there. Similarly, clothing has seasonal and regional aspects, so that thinner materials and fewer layers of clothing are generally worn in warmer seasons and regions than in colder ones.
Clothing protects people against many things that might injure the uncovered human body. Clothes act as protection from the elements, including rain, snow and wind and other weather conditions, as well as from the sun. Clothes also reduce the level of risk during activity, such as work or sport. Clothing at times is worn as protection from specific environmental hazards, such as insects, noxious chemicals, weapons, and contact with abrasive substances. Conversely, clothing may protect the environment from the clothing wearer, as with doctors wearing medical scrubs.
See also: http://en.wikipedia.org/wiki/Thermal_insulation
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)