A separating zipper in the same length as the front of your hoodie, or longer. My Lifehacker hoodie was 25.5 inches from neckline to bottom, so I bought a 26-inch zipper like this one for about $4.

One PS editor tries the bestselling Lululemon Scuba Oversized Half-Zip Hoodie to see if it’s worth the hype. It's soft, breathable, and flattering.