Homemade bumpers
 

What material have people used to make bumpers out of? ABS? Nylon?

kydex.

As above Kydex , eBay has plenty , 3mm works well , can be softened in the oven and easily formed or a heat gun works as well, you can score it with a craft knife and it cracks along the score line just like Lexan but a lot tougher or you can saw it but don't use a jigsaw as it melts it .Standard bumper material on quite a few classics ,Kyosho Scorpion range , Hirobo Zerda , Ayk Bobcat and Sidewinder and of course the Yokomo YZ10/870C range as well , they all and many more had Kydex bumpers .

So you basically shape it yourself or is this via a 3d printer?

DIY dead easy

Kydex for me too. 3mm, 2mm is too flexy. Great tip about the oven, I'll give that a try.

It comes in sheets of different thicknesses but for a bumper 3mm is best , its a fairly soft plastic that's very impact resistant , it can be heated and formed or bent and when it cools retains the shape , its similar to Lexan in the way it can be shaped but a quite different sort of plastic , more like nylon or polythene .
People use it for making knife sheaths and gun holsters , there are loads of tutorials on YouTube on how to use it .