| Polyurethane foam, spray-applied by The Ex-El Co., Inc., creates the shell. The shell is now approximately 5-1/4 inches thick (4-1/2 inches of foam sprayed over the wire membrane). Foam provides the rigidity, strength, and insulation (with an R-factor of R-6/in), and it waterproofs the shell as well.
During application, the liquid pre-foam material (3lb. density) easily penetrated the many layers of wire mesh, fused them together, and glued the mesh to the wooden frames. The shell's dimensional stability and tensile strength is an added bonus.
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