Fiber Glass

Fiber glass is used as air filter media, and fiber glass in walls and ceilings behaves much as the fiber glass in an air filter. Air rushes right through it. When fiber glass-insulated walls are opened the batts are usually found to be covered by dust, just as an air filter would be. Additional materials to control air movement are essential  in fiberglass insulated building assemblies. In addition, extreme care must be taken to seal all areas around pipes, windows, electrical boxes, and along studs in fiberglass insulated walls. High R-values won't assure comfort or energy savings if cold air (or hot air) can leak into the building around and through the insulation. It is possible, but difficult, to build tight fiber glass-insulated assemblies. By using overlapping foam sheathing, a separate air barrier, and extensive amounts of tape, caulk, and injected foam sealant fairly tight walls and ceilings can be constructed under controlled conditions. Builders often are reluctant to use these measures. The extra materials and the painstaking attention to details add considerably to the cost of the building. Why not just use insulation that "automatically" tightens walls and ceilings?