Darth Vader’s suit changed throughout the OT. In ANH it looked kind of clumsy and plastic like seen here: http://www.jedidefender.com/collect92/vader anh.jpg

In Empire they definitely stepped it up in looks. Gave his should plate a shinier and more polished look as well as adding illuminating buttons to his chest plate and a glossier looking helmet: http://i826.photobucket.com/albums/zz190/ThePropDen/e34d01ea.jpg

In Jedi though, I think is when Darth Vader was taken to the next level. The changes to his helmet & suit were subtle, but there is something about his look, it transcends time: http://images4.fanpop.com/image/photos/18300000/Star-Wars-Episode-VI-Return-Of-The-Jedi-Darth-Vader-darth-vader-18356369-1050-656.jpg

I have a few questions:

Does anybody know the technical differences between Darth Vader’s suit in ANH, ESB, & ROTJ?
Why did they decided to make a new suit for Empire & Jedi. Wouldn’t the ones made for ANH due fine?
Was it because they had multiple actors playing Darht Vader in ROTJ? (Sebastian Shaw is one I know of but there may have been others)

That still doesn’t explain though why they changed Darht Vader’s suit in ESB because as far as I know David Prowse played the character the whole time.

Dath Vader’s helmet was in reality made out of plastic of course, but I assume in the movies it was supposed to be interpreted as being made out of metal.