How can a sports shirt move sweat away from your skin?

A shirt can develop a broad damp patch even when sweat first reached it in a few small spots. Liquid has spread through tiny spaces among its fibers. This movement, called wicking, is one reason the structure of sports clothing matters as much as its color or softness.

Water molecules attract one another and interact with the surfaces they touch. In narrow spaces that water can wet, these interactions allow capillary action to draw liquid along the gaps. The fibers need not act like little drinking straws with hollow centers: spaces between fibers and yarns can provide the routes. Fiber shape, surface treatment and the arrangement of the fabric all influence the result.

Spreading liquid over a larger exposed area can help it evaporate, provided water vapor can escape into the surrounding air. Wicking and evaporation are different processes. The first moves liquid within the fabric; the second changes liquid water into vapor. A shirt can wick well and still remain wet when the air is very humid or the fabric is covered by another layer.

Evaporation requires energy. When sweat evaporates from skin, it takes heat directly from the skin; when it evaporates from clothing, heat can come from the garment, surrounding air and body through their thermal contact. Moving sweat does not automatically guarantee the same amount of body cooling. Air movement, fit and weather also matter.

That makes a sports shirt a small transport system. It must handle liquid water, water vapor, air and heat. A label naming a fiber alone cannot describe all of those paths. The useful question is how the complete fabric allows moisture and energy to move.