Riddell mini-helmet

Riddell mini-helmets were a set of helmets made by Riddell, a sports souvenir company.

Although primarily focusing on sport-related helmets and equipment such as football helmets, there was a variety based on the Star Wars franchise released in 2003/2004. Only five were created before they were replaced with MR, which included Darth Vader's helmet (which also had both the mask and helmet removable, as in Return of the Jedi), Boba Fett's helmet, a ROTJ-era Stormtrooper helmet, Luke's X-wing helmet, and C-3PO's head. The Stormtrooper helmet was the rarest, with Boba Fett being second rarest.

Each helmet also came with some blueprints that described the functions of the helmet in-universe.

Behind the scenes
According to Daniel Wallace in his tie-in blog to the release of Darth Vader: A 3-D Reconstruction Log, the Reifflex cellular padding was first mentioned in one of the blueprints for the helmets.