Abstract: A sprayed on, semi-rigid, substantially closed cell foam insulation which forms an insulative layer directly on an interior wall or internal structural member associated with a skin of an aircraft fuselage. The foam insulation may comprise a polyurethane, substantially closed cell foam which is sprayed on to the interior wall of the fuselage to form a layer having a thickness of between about 0.25 inch-1.5 inch and a weight of between about 2 lbs. per cubic foot to about 3 lbs per cubic foot. The insulative layer forms a thermal and acoustic barrier and is highly resistant to the absorption of condensation and humidity. The foam insulation, being sprayed on, can be installed much more quickly than conventional blanket-type insulation material and with significantly less cost.