Part 1: Rapid Prototyping the Helmet
Part 2: the Hard Parts
The whole suit is supposed to look like it's made of metal (I know, a gold-titanium alloy). So for me nothing detracts from an otherwise well-done Ironman costume like gaps around the joints showing that there's just a spandex-clad nerd inside.
While I'm not about to go through the trouble of engineering a series of compression articulations for these areas, I still need to fill them in with something that I can convincingly paint to look the part.
This is why I needed to make the rubber bits:

To see how I made these parts, read on...