Duraglass substitute for fiber mat/resin?

I recently watched a few dvds my friend purchased from caraudiohelp.com. In the fiberglass video, during the sub enclosure install, I noticed how they only used one layer of fleece cloth and resin then proceeded to use duraglass body filler as opposed to fiberglass mat and resin as I've seen in other tutorials. Through your experiences, is this duraglass filler a viable substitute to the recommended 6 layers/oz of fiberglass matting? Thanks

Duraglass is mush more brittle than fiberglass and should not be used in place of fiberglass when used for high strength areas, duraglass is fine for small things like tweeter pods or something that doesnt require a whole lot of strength.