This type of airborne helmet was made specifically by the Riddell company for training paratroopers. The Riddell company had originally invented a similar style of helmet for football. At the time, it was revolutionary since this was still the era when football players wore leather helmets. They took this new technology and incorporated into this type of helmet to be used during the jump school training for paratroopers. Period pictures show this style of helmet being worn by the earliest members of the US airborne forces.
The leather flap on the chinstrap was designed to be unfurled and tucked into the neck of the uniform, in order to protect the chin of the paratrooper from branches during his jump. The leather around the back edge of the helmet was to protect the neck area from the rough edge.
This particular helmet came from the same paratrooper who also owned the M41 jump suit and Hawley paratrooper helmet liner from previous posts on this blog.