Here is a picture I got from the internet of the actual undersuits used on the show. I believe they are some sort of rubber.
I ordered a body suit off of eBay from China. I wanted a suit without a face, which I couldn’t find locally. The good thing about the suit from china was that I sent my measurements, and they made it custom, at about the same cost as what I could have bought at a Halloween store. The down side, is that I ended up having to resew some of the seams, as they were cheaply done.
For the tubing I used round foam insulation tubing called “caulk backer rod,” from my local home improvement store. I also used strips of craft foam.
For the tubing, I sliced it in half with a razor blade, and then scored it, each tube a little differently. Then I shot it with a quick burst from the heat gun. Too long and it shrivels away to a pile of goo. Trust me on this. I did a similar technique on the foam, cut into strips, slice with a pattern, hit with a heat gun to open the pattern.
This foam tubing wasn’t super expensive but you needed a lot to cover the suit, so I just covered the suit where it would be showing. I also didn’t put the tubing in the friction areas, like under my arms or between my legs, as the stuff is rather fragile and would just rub to pieces.
I gave them all a hit of plasti-dip. If I had this to do again, I think I would have skipped this, as the dip didn’t really seem to do that much. Maybe if I had done multiple layers – but that stuff is expensive, so I didn’t. I ended up going back latter and touching up with black spray paint. (I’m not sure what the neighbors thought, but when my son went out to jump on the trampoline, it freaked him out.)
Even now, the undersuit is a fragile thing. Every time I put it on I’m flaking off paint or ripping tubing. Every few wears I have to re-glue on pieces and touch-up paint. I’m not sure how to avoid this problem with the materials I’ve chosen to work with. You have been warned.
I know that some Cyberman cosplayers don’t take time to make an undersuit, but I feel this is a big mistake. The undersuit adds authenticity and depth to the suit.