Textiles are made with yarn, a spun thread used in both knitted and woven fabrics. With every wash, wear and the ticking of time, the tiny fibers that make up the yarn break. Thanks to not-so-fabulous friction, these "broken" fibers ball up to create pills (aka: fuzz balls) on the fabric’s surface. They then proliferate in high-friction areas like the under-arms, sleeves, bust area, and inner thighs. Yay.
Virtually all fabrics pill to some degree. The extent to which it's noticeable varies and it depends on 1) the fiber content, 2) the fabric structure, and 3) wash and care.
Fiber content makes reference to what the fiber is actually made of. In general terms, we're talking natural fibers (cotton, linen, wool and silk to name a few), synthetic fibers (acrylic, polyester, lycra and others) and blends (Ex: cotton-polyester blend or a wool-acrylic blend).
Some fibers are more pill-prone than others. As a general rule, natural fibers pill less than synthetics as the individual strands that make up the yarn are both shorter and less robust. As a result, broken fibers are more likely to break off before they pill and the fuzz balls that do accumulate are more easily removed.
Synthetics, on the other hand, make for some tough fuzz. The long, robust strands found in these yarns tend to pull and stretch into pills rather than break off.
Knitted fabrics are made by looping yarn; woven fabrics are made by interlacing yarn at right angles. Knits (yes, even the really expensive ones) are looser in construction, leaving them more susceptible to friction and thus more prone to pilling. But, we love them for their forgiving stretch, deliberate textures and intricate pattern play (hello chunky cable knit!).
Just as important as “what’s in it” and “how it’s made” is the tender loving care that you give each garment. Machine washing and drying are two major sources of friction so it’s important to read care labels carefully and launder your garments accordingly. For clothes that look new longer, use a mild detergent and wash them inside-out. As an extra precaution, skip the dryer and hang or lay flat to dry.