When we exercise we all make different choices about what we wear - whether it's a decade-old baggy T-shirt, last season's football strip, or high-tech performance sports gear that's been specially designed for the task at hand.
But if we're being honest with ourselves we've probably all noticed that there are certain items in our gym bags that always smell worse than others. And now and then most of us have probably wondered why.
Studies have actually been done comparing the smelliness of different fabrics. Two such studies, at the University of Alberta and the University of Ghent, used highly trained odour analysts to sniff various fabrics after they'd been worn, and they both came to the conclusion that polyester gets much smellier than natural fibres like cotton or wool.