What is the difference between bondo and fiber glass?
What would you guys use if not bondo or fiber glass?
Is there any better product than bondo?

 

Fiberglass filler (fiberfill) is basicly epoxy with fiberglass strands in it. It seals the surface fairly well against corrosion. It is used as a cheap fix on metal when welding isn't practical and the damaged area is too deep for regular filler, and also for filling holes greater than about 1/8". It is, of course, also used to repair fiberglass. It needs a minimum thickness of at least a couple mm because the strands make it difficult to spread thin. Because of this, it comes in long and short strand versions. Short can spread thinner and is easier to work with. Long is stronger for larger patches but the spreader tugs on the fibers more while applying. Typical filler spreads and sands much, much more easily and needs to be used on top of the fiberfill to continue leveling the surface. Bondo is a brand name that makes normal filler, fiberfill and alot of other types. A non-professional should probably use Bondo's premium filler as it is available at most parts stores. A step up from fiberfill would be something like Kevlar filler or a similar high-tech and expensive substance. Check out Bondo's site and the paint & body forum here for more info.