Seriously, if you look at NCR Fatigues, which has none of the plates on it, it's 26 pounds, what are those clothes made from? Steel? :blink:
They are made of http://en.wikipedia.org/wiki/Vertex_%28computer_graphics%29.
If you however want to know what they should represent, I'll say they represent something like http://en.wikipedia.org/wiki/Coat_of_plates also known as http://en.wikipedia.org/wiki/Brigandine sometimes. In essence steel or other plates under textile or leather which holds them together.