Wicking: Synthetic Fabrics
Capillary action also occurs with synthetic performance underwear. Here’s how:
- An active person wearing a polyester T-shirt begins to sweat.
- A high-humidity “microclimate” is created between the person’s sweating skin and the shirt covering the skin.
- Perspiration vapour and moisture condense on the garment’s interior (its underside).
- Because everything in nature moves toward equilibrium, the high-humidity air mass between skin and garment will seek a path to a lower-humidity environment. The difference (gradient) between temperature and humidity on both sides of the garment becomes the driving force that moves the warmer, wetter air beneath the garment toward the cooler, dryer air on the outside.
- Wicking takes place when perspiration moisture travels along the surface of the fibre but is not absorbed into the fibre. (Synthetic fibres are, essentially, plastic—and virtually non-absorbent). Moisture escapes to the outside through the interstitial spaces (the miniscule holes) between the knitted yarns.
- Moisture is dispersed across the fabric’s exterior, where it evaporates after contacting the lower-humidity environment outside the shirt.
Wicking is enhanced by:
- Fibres with an altered texture (roughened or grooved) can transport moisture more quickly.
- Fabrics such as Polartec PowerDry use a 2-sided “bi-component” construction. Such fabrics typically position thinner yarns closer to the skin (sometimes dotted with moisture-collecting “touch spots”) and place larger yarns on the garment’s exterior, providing more surface area for moisture dispersal and evaporation
- Some type of chemical finish is applied to nearly every synthetic fabric in order to boost wicking performance. The finish usually convey some degree of hydrophilic (water-attracting) attributes to polyester, allowing it to more speedily draw moisture along its non-absorbent fibres and transport it to the garment’s exterior.
Note: Polyester, while synthetic, does have a very small absorption rate, roughly 0.4% of its weight. (In contrast, cotton can absorb 7% of its weight.) Polyester’s absorption rate is so minimal that it is generally regarded as non-absorbent.