If you have a favorite warm-weather button-up, ruffled top, or shirt dress that’s crisp, lightweight, and made from cotton, it’s probably poplin. Casual and polished, cotton poplin is a staple alongside other seasonal favorites like linen, keeping you cool while remaining work-appropriate.We recommend cotton poplin pieces — from a little black dress to a polished button-up shirt — in multiple guides. Style writer Zoe Vanderweide, who wrote our guide to the best little black dresses, says that she likes the fabric because it is “light, but not thin or whispery,” with “enough structure to maintain a nice shape and drape.”But not every fabric that looks or feels like cotton poplin is, in fact, cotton poplin; the market is flooded with impostors that mimic this fabric but lack the qualities that make it so versatile. Here’s what to know about the shirting staple and how to choose the real thing.