The "add-on" hooded sweatshirt design, as the name suggests, involves sewing the hood onto the neckline of a crewneck sweatshirt "afterwards."
Most of these models have a cotton drawstring, allowing you to pull it over your head and tie the string. Older models, however, have a snap button closure like this one. This design is a remnant of the heavy construction used to secure hoods made of wool fabric, and is an extremely rare detail for a cotton sweatshirt.
