Almost all running and fitness apparel claim to breathe and wick - two concepts that cause confusion for many. The breathability of a fabric refers to its ability to allow moisture vapor to be transmitted through it. Simply put, its the fabric's ability to evaporate your sweat as you get hot. Wicking refers to a fabric's ability to pull moisture away from your body and keep you comfortable. Therefore, with high-performance running and fitness apparel, manufacturer's are always seeking the latest "technical" fabrics that wick and breathe very effectively so that athletes can maintain comfort and maximize performance.
Most of today's "technical" fabrics are made of synthetics, like nylon and polyester. Synthetics, by nature, have no inherent wicking capabilities. A microscopic look of a polyester fiber yields a smooth plastic fiber that is purely hydrophobic (water repelling). 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 garment's ability to wick sweat. However, many manufacturers simply use untreated polyester fibers and are totally dependent on the weave of the fabric to channel sweat away from the body and onto the fabric. Through the channeling of sweat onto a greater surface area (i.e., the shirt) made of hydrophobic polyester fibers, the moisture is able to evaporate faster than it would on your body. We call this passive moisture management.
As it pertains to breathability, synthetics are actually quite poor because they are essentially solid plastic fibers. Tight knit polyesters are actually very warm to wear and to compensate for this, running and fitness apparel are made of fabrics that are very thin. One of the biggest drawbacks to thin polyester is that it provides little protection from the sun's harmful UV rays - a concern for endurance athletes.
In contrast, there is a natural fiber that inherently possesses superior breathability and wicking properties - Merino wool. Merino 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. It is this unique structure that enables Merino to employ active moisture management. 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 moving sweat away from the skin and releasing it as vapor. In fact, in CSIRO testing, Merino fabric was shown to transport 27% more uncomfortable sweat away from the skin than a synthetic fabric. Furthermore, because of the hydrophobic exterior of Merino fibers, it delivers the channeling and greater surface area, like synthetics, to speed sweat evaporation. 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. Greater comfort is key to higher athletic performance. Lastly, Merino fabrics can be made very light and thin, comparable to the lightest synthetics, but unlike synthetics, they deliver the added benefit of sun protection. At PULSE, our lightweight Merino fabrics naturally provide UPF 50+ protection.