tool for body curves

I drug home a 67 Bel 1, repaired rear qtr with the only patches available, pretty sorry stuff. I never had one, but seems like years ago I saw a tool that will mold to the body curve to help get the curve right with filler. weems like it was made of a foam? type material? anyone one know what i'm talking about and where to find one. I looked under auto body tool and eastwood and did not see anything.
I need t make that rounded curve on the rear qtr decent! I m not good with filler and curves i admit!!!!!!