You never understood why bodysuits went out of style.

A piece of fabric that rides up your ass and snaps at your crotch is pretty awesome.

The ’80s fashion is making a comeback, thanks to Heartloom, a new collection of casualwear designed by Katy Lee, whose resume includes Marc Jacobs, Vivienne Tam, and Heatherette.

At the center of the layerable line: a bodysuit. The onesie has been updated with a cinched waist, pleats, and peek-a-boo bow at the neck. It can be worn as a tank — or sans pants as cutesy lingerie.

The rest of the laid-back oeuvre consists of rompers (the denim version is a standout), jeans, tees, dresses, and oversize hoodies — all constructed with soft, high-quality fabric.

A stellar detail: Everything (except coats) ranges $59-$199.

Retro pricing, too.

Available at Atrium, 1931 Collins Avenue, South Beach (305-695-0757); online at singer22.com. To see styles, go to heartloom.com.