Check out the prototype X-Wing helmet shown here.
http://www.starwarshelmets.com/original_rebel_pilot_helmets.htm
Where were you in '77?
Does that one near the top have a gas mask attached to it? Looks like they thought that out at one point and then decided to ditch it for cinematic reasons.
IT'S MY TRILOGY, AND I WANT IT NOW!
"[George Lucas] rebooted the franchise in 1997 without telling anyone." -skyjedi2005
"Yeah, well, George says a lot of things..." a young 1997 xhonzi on RASSM
"They're my movies." -George Lucas. 19 people won oscars for their work on Star Wars (1977) and George Lucas wasn't one of them.
It's also possible that they have a quick-don oxygen mask system that snaps into they're helmet with one motion. This is how airline oxygen masks work. They don't have a helmet to snap into, but the oxygen mask hangs within easy reach of each pilot & can be grabbed & put on with one hand in about a second. That way, you don't have to wear the uncomforatable mask all the time, but in a sudden decompression, you can have oxygen on almost immediately.
putting on a quick don mask: