Demystifying the Claims in the Marketplace
A phrase that has been popularized by fitness clothing manufacturers in recent years is "wicking". Wicking has also been popularly described as a fabric's ability to "breathe". Both terms, simply, refer to a fabric's ability to pull moisture (a.k.a. sweat) away from a person's body and onto the surface of the fabric for quick evaporation. Wicking is accomplished by a combination of the fiber used in the fabric and the weave used in the manufacturing process. Obviously, the more porous the fabric, the greater perception one has of a fabric's wicking ability, but is the fabric actually wicking?
If you take this to the extreme, all of us would be doing our workouts in fishnet right? Well obviously this has its drawbacks, like...well you get the picture. Plus, in actuality, a shirt made of fishnet would actually be doing very little wicking because our skin would be exposed to air and evaporating its sweat as it naturally would. The fishnet shirt itself would actually be doing very little in the process, but some would mistakenly say that the fishnet shirt really "wicks" or "breathes".
So as you can imagine, as we go from fishnet to a tighter weave in fabric, the less skin we have exposed to the air and thereby restricting it's ability to evaporate its own sweat. Therein lies the challenge for fitness clothes - providing the person with the necessary coverage while keeping them comfortable by moving sweat away and evaporating it (i.e., wicking).
Synthetics, like polyester, by nature have no inherent wicking capabilities. A microscopic look of a polyester fiber yields a smooth plastic fiber. To give it wicking capabilities, some manufacturers apply a chemical coating to the polyester fiber to give it the ability to attract or pull moisture away from one's skin. This, combined with various weaving techniques increases a polyester garments ability to wick sweat. However, many manufacturers simply use untreated polyester fibers and are totally dependent on the weave of the fabric to enable air to pass thru to the skin to evaporate sweat (i.e., there actually is no wicking of sweat away from your skin). In this case, the polyester fabric is essentially a passive, plastic coating covering your skin.
In contrast, Merino wool fibers have a complex, scaly structure with a hydrophilic (water holding) interior, known as the cortex and a hydrophobic (water repelling) exterior, known as the cuticle. In other words, Merino fibers naturally have "active" properties unlike synthetics. The hydrophilic core of the Merino fiber has an amazing capacity to absorb liquid - up to 35% of its own weight - so it's better than synthetics at removing sweat from the skin, moving it away, and releasing it as vapour. In fact, in CSIRO testing, Merino wool fabric was shown to transport 27% more uncomfortable sweat away from the skin than a synthetic fabric. Not only does this mean that Merino is better at keeping the skin dry and comfortable during workouts, but this process of evaporation actually produces a drop in temperature which acts to make the "micro-climate" between the fabric and one's skin even more comfortable.