A little ingenuity can replace a crane when installing roof panels. This 4x16-foot panel is 4 1/2 inches thick and weighs in at about 250 pounds. frame. A decade later, after much experimentation, the stressed-skin panel has become our preferred insulation system. Recipe for a onestep shell: Plan for minimal waste, measure and cut with precision, and be sure to seal 'em tight. A stressed-skin panel is nothing more than a sandwich of a thick core material bonded to two thin outer skins. The structural principle is similar to that of an I-beam; the outer skins serve as the flanges of the beam, while the insulation core performs the role of the I-beam web. The panels we now use have a polyurethane core