The entire M-19 Flying Squirrel is constructed using rigid extruded polystyrene board with a fiberglass skin. Either pink Owens-Corning "Foamular" or blue Dow "Styrofoam" extruded board is used for construction, 3/4" thickness, with no plastic film. It is glassed in the same fashion as the urethane foam boards... microslurry goes on wet, then wetted out glass is laid over and squeegee'd into place. Wings, control surfaces, fuselage, everything on the airplane uses this board.
As others have noted (or have discovered the hard way), the main caveat when working with extruded polystyrene board is to keep any hydrocarbons, solvents, or fuels away from it. If you want to see a disappearing act, just get some gasoline, MEK, or even spray paint near the foam board and *presto*!- it's gone. In fact, this can be used to advantage when forming a fiberglass part over a foam form. When the layup is cured, just slosh a little gasoline around inside it and the foam will dissolve away. My M-19 is being constructed using the pink board and AeroPoxy laminating resin, but the wet cell wing fuel tanks will use vinylester for fuel resistance. Oscar Zuniga Medford, OR
