Abstract: A vehicle body pillar has a cavity therein through which air flow creating undesirable noise and in which moisture and fluids such as water are not to be collected. An expandable sealant plug is inserted therein and retained in place. The sealant material forming the plug is later expandable under controlled conditions. It is preferably expandable under temperatures of about 275.degree. F. to 400.degree. F. over a period of time. Preferably during the electro-coated paint baking and curing operation, the sealant is exposed to appropriate temperatures for sufficient time to expand the sealant about 800% and cure it, sealing the cavity so as to prevent the flow of air through it. The expanded sealant also effectively blocks the intrusion of fluids such as water, minimizing corrosion within the pillar.