Foamseal is no longer producing automotive foam. However, they distributed FOMO brand anyway for the automotive division which IS still sold (you can find it everywhere on google). I is a 3lb./cu.ft. closed cell foam. There is also another brand foam I found on a supra forum that is used in filling molds for making models that is a 15lb./cu.ft. design. Much denser for rigidity, but also will add more weight to your car. You will also have to search for it as I don't remember the name. If you are that serious about chassis rigidity, I would suggest to just stitch weld the whole car (not for street cars because this affects the "crumple zones" for safety).
