Nearly all of the figures on the Kid Robot site are rotationally-molded (roto-molded) vinyl. To my knowledge, that’s the least expensive way to do tooling for short runs. And, you can mold pretty much any form you want - undercuts and all. The results are beautiful.
Some of the figures may include injection-molded parts, usually out of vinyl as well. Vinyl takes pad-prints and spray ops really well and the colors are always nice and vibrant.