Question... It occurred to me something... more of a brain-teaser. Form all the space-suits I've seen in most Sci-Fi(s)... Just how does the Neck-Seal(and just as important, what does it LOOK like) when (FUNCTIONALLY) attached to the helmet to make a perfect-seal in whatever environment. I've been hunting for the OFFICIAL description without much luck and asking around if anyone has any clue as to how it all works, in this case, a 40K Space Marine Helmet to Neck-Seal...
As I am neither the cosplayer in this photo nor an expert in the Warhammer 40K universe, I'll have to guess.
One of the best examples of a Sci-Fi suit being sealed without involving force fields would have to be the metal collars used in the remake Battlestar Galactica pilot suits. The pilot suit would go up to a metal collar in the neck area. When the helmet is put on, the metal collar would lock into the helmet, creating a fully sealed environment.
Sadly, they would never do that unless someone marches into their office and threatened them to in power armour... Or maybe drove the Rhino they made into their main office or Relic's office in Vancouver