Perforation is one of the subtlest ways for designers to reference athleticwear. It alludes to sneakers and old-school sports jerseys, yet you only perceive it at close range, unlike, say, racing stripes or JETER 2. Of all materials, leather lends itself most obviously to perforation. But for spring, designers have punched holes in everything from woven cotton to bonded paper. Even knitwear is breathing a little easier.