What makes it a classic: the tight, vertical ridged pattern that makes the garment better able to retain its shape, keep the AC out (without necessarily being thicker), and have a sexy, sporty cling. And what makes it especially cool now: the return of body-con – and how it lets you channel the look tastefully, be it a bookish button-down top (Bottega Veneta), military-inspired sweater (Versus) or midi dress with a knee-high slit (Altuzarra).