Eugene,

 

It's also called closed cell foam.  Most upholstery shops carry it, and any auto upholstery shop will have it in 1/8" nand 1/4".  Be sure to sand it to remove the thin shiny layer.  That layer can separate from the foam.  A good sanding job leaves it feeling like suede.  It does a great job of smoothing out the irregularities on the fuselage top.  Try not to get glue on the low spots when you spray the glue on the fuselage interior and the foam will bridge those areas instead of following the contour down into the low spots.  It also doesn't hurt to use a heavy duty adhesive, instead of the regular "General Trim Adhesive", because the top of the fuselage is exposed to a lot of direct sunlight and can weaken the bond of the regular adhesive.

 

Mike Easley

Colorado Springs