Thermoregulation is the natural mechanism by which the body attempts to balance heat gain (and heat loss) in order to maintain a constant normal body temperature when exposed to variations in the cooling power of the external medium. Many things happen when the body overheats, but the average person never notices. The hairs on the skin lay flat, preventing heat from being trapped by the layer of still air between the hairs. A relaxation of smooth muscle in arteriole walls allows increased blood flow to the superficial capillaries in the skin, increasing heat loss by radiation and conduction. But the primary way the body cools itself is sweating, which achieves heat loss through evaporation.
Clothing keeps you hot
Any article of clothing, worn during exposure to high temperatures and/or during periods of exertion, will inhibit the body’s natural thermoregulation efficiency. Nothing that can be worn next to the skin or on the body will speed the body’s cooling systems as fast as bare skin. Occupationally, however, shedding clothing is often not an option. Plus, when multiple risks occur simultaneously — like extremely high temperatures and the risk of exposure to fire, explosion or electric arc — we invite a greater risk of burn injury in solving excessive heat by removing clothing.
Wick away moisture
The evaporation of sweat — not sweat itself — achieves the cooling function. For protective garments to keep from impeding this process, they must absorb and wick moisture from the skin and transport it away from the body for evaporation.
Historically, the textile industry has relied on many natural and commodity fibers that have exceptional absorption properties. For example, a 100-percent cotton T-shirt will absorb very large amounts of moisture. But even in summertime, 100-percent cotton garments remain wet for hours. The wicking and evaporative qualities of all-cotton solutions actually can raise the risk of heat stress. Water, after all, is a very good insulator, which means when the body is effectively wrapped in, or insulated by, water, the body’s objective of cooling itself is further inhibited.
New fabric technology
Today, garments made with a combination of waterloving viscous fibers, like cotton, with water-resistant fibers come close to eliminating the impediments to the body’s natural thermoregulating systems. This fabric technology breakthrough has spawned a global “performance wear” industry featuring clothing that dries four time faster than 100-percent cotton.
Manufacturers have innovated with the use of water-resistant fibers that are also naturally self-extinguishing. Occupational wear is now available that not only greatly reduces the risk of heat stress caused or advanced by next-to-skin and outer-wear garments, but that also reduces the risk of burn injury.
Wicking technology
How exactly is wicking and drying optimized by the new technology? The interfaces between the majority of fast-drying, water-resistant fibers and the minority of wicking and water-loving fibers drive moisture out of the fabric. The combination of these fibers speeds the transport of moisture throughout the fabric, which allows airflow to evaporate moisture more effectively.
The result is a fabric blend that quickly, evenly and constantly spreads moisture throughout the whole garment. This maximizes the surface area for airflow, which is the essential element in fast evaporation. In combination, wicking, absorption, moisture transfer and distribution work together to keep users cool during activity and then quickly reduce any residual moisture during inactive phases. Of course, keeping moisture away from the skin has other benefits. Workers exposed to an accidental release of very intense heat, for example, risk steam burns if moisture next to their skin even temporarily approaches 212°F. Moisture next to the skin for extended periods of time is also a leading source of microbial infection.
