In 40 years we went from the interior to the exterior withair barriers. And we went from combining the vapor barrier with the air barrieron the inside to combining the water control layer with the air barrier on theoutside. We went from films on the inside to sheet goods on the inside. Then wewent from films on the outside to sheet goods on the outside. We went fromcaulking and the black death on the inside to tapes and fluid-applied jointsystems on the outside. Joe discusses the evolution and possible future of airbarriers.