As a note, genuine US issue flight suits (or commercial variants of US issue) are made from Nomex which is a fire resistant material. This may or may not be screen accurate but it would be more authentic since they would almost certainly be wearing flame resistant clothing aboard a starship, just like they do on surface ships and subs in real life. However, for comfort and/or cost you'll want to consider buying flightsuits made from cotton since I don't think that fires are much of a concern at most cons. Very few people will be able to tell the difference and even fewer will care.