Screen-used dummy EVA suit helmet used instead of the hero prop.
Typically used as set decoration or for scenes where the hero
helmet was not needed.

Hero Helmets and Background Helmets

So far, only 5 Hero Helmets were made,

as appear on the teem photo at Major Tom wall in the Pilot.

Later the team photo was replaced, showing 8 helmets, but seems a photo montage.

On the famous scene bellow, Steven and Nadia have a Background Helmet, but I don't think Evram have any helmet.