I got the foam from Aircraft Spruce http://www.aircraftspruce.ca/catalog/appages/supersoundproofsheet.php This material is excellent for reducing noise levels in all types of certificated and home built aircraft. It is a closed cell vinyl insulating material which will not absorb water or oil. Has fire retardant qualities and meets FAR 25.853a Appendix F, Pt1. It is smooth on one side for easy attachment to the inside cabin skins, sides, top and front firewall.
Excellent for helicopters as well. Furnished in bulk 48" wide sheet, it is easily cut by scissors and attached with contact cement. Available in black only.
I got 20'x48" wide. I didn't use it all - probably have about 5' left, so I probably used about 720 sq ft.
