hi! diy_pads has a lot of folks who make their own (i'm not one yet), and mostly it looks like they use cotton flannel, terrycloth and microfiber, you can get the first two at any craft store, and microfiber can be found in automotive and hardware inexpensively.

I haven't made any, but I own a few that are closed by snaps instead of hook and loop tape. When you ask "what keeps them from twisting around" I'm guessing you mean so that the pad is on the underside of the undies? I don't know *what* keeps it from doing so, but I've never had a problem!