I was watching a TV program where they were building a car body. They used big blocks of foam, cut and sanded it down to size, covered it with fiberglass matte and resin, and made a fender. Where can you buy this foam and what is it called?
Look at the on line catologue or request one from Fiberglass Coatings inc in Florida, or www.fgci.com. I cannot remember the name of the foam at the moment, Arghhhhh, I hate that when that happens. It is used for patterns as well as actual one off projects. It can be shaped nicely with a high speed cutting tool or grinder and it can be cut with a variety of tools. It sands well too due to the density.
The only foam that I would think it is would be Extruded Polystyrene foam, it is used as a base in hovercrafts and planes, I dont know exactly where to buy it, I bought some at Lowe's but it was very thin, universal hovercraft sells sheets up to 3" thick I will put a link, but please let me know if I am not allowed to.
Common 2" foam insulation you can get at any lumber yard will work just fine. Glue it together with construction adhesive, bondo over it and you have yourself a true surface buck. Now, to get even more in depth, use plywood to create a station buck, fill the voids with the foam insulation, file it to shape, bondo the entire surface, sand it smooth. At this point, make a flexible shape patern, then remove the foam, being careful not to pul the bondo loose from the edges of the plywood. This will allow you to see how the metal is fitting the buck from the back side. For more information, go to www.metalmeet.com and search for keywords found in this message. If you need more help, just ask.
the foam you refer to is rigid urethane foam. it comes in sheets, blocks and liquid a/b type. it also comes in different density, measured in lbs per cubic foot. 2lbs being very light like the white foam balls you may find at an arts and crafts store. you can also find it as high as 48lbs which more resembles a wood plank. somewhere around 15 lbs is what you want. it is also called prototyping foam. since its urethane, its chemical resistant so when you are done shaping you can primer directly on it or fill it with bondo or whatever you want. lots of companies make it, do a search on google for last-a-foam fr-7100, proto foam, proofboard etc.
Polystyrene will dissolve when polyester resin is applied to it. For polystyrene you must use epoxy resin. The stuff you are talking about is polyurethane, fiberglass resin (polyester) will not harm it.