Hannah dresses like a “sad, limp, little glow worm”

This look really throws me. What the hell is she wearing? And why is there no explanation? Is this the new Snuggie/Forever Lazy? A Google search for “sleeping bag vest hood” yielded nothing confirmatory. I just don’t get why it’s this full body sleeping bag but then the arms are bare. Is it some sort of sweat-inducing weight loss tool (since she was doing a workout video in the previous scene)? Someone explain? UPDATE: Jenn Rogien has explained, to The Cut:

It’s a sleeping bag, with armholes and a hood. And, believe it or not, it was actually in the script that Hannah was wearing a sleeping bag with armholes. I had no idea that such a thing actually existed. I was gearing up to make it myself, or buy an actual sleeping bag and alter it to have armholes, and then one of my team members went online and found company that makes them, called Poler.