Fiber Reinforced Plastic, see http://en.wikipedia.org/wiki/Fibre-reinforced_plastic . Most often found in our industry in laminate sheetgood form on roadcases or ATA cases. May also be used as a structural component where non-conductivity and corrosive-resistance is desired (such as underwater).
http://www.eplastics.com/Plastic/Flat_Fiberglass_Sheet/FRPWHT0-09048X120
http://www.eplastics.com/Plastic/Flat_Fiberglass_Sheet/FRPWHT0-09048X120