What is your preferred foam/thermoplastic/cardboard sheet thickness?

Hi all, I wanted to get a sense of what people prefer to use when they hand make props. I've been doing a lot of work in 3d modeling recently, and I usually end up with detailed templates during the CAD process. I can export these pretty easily to layered cutting templates. I see a lot of 2-6mm sheets available, but I'm not sure what the consensus is.

So, what sheet thickness do you all like to use?