As discussed in Chap. 4, the need for vapor retarders and their proper location within a wall assembly are influenced by the interior and exterior environmental conditions, as well as the wall’s thermal and vapor flow characteristics. When installing loose-fill insulations, a material such as 6-mil (0.006-in) polyethylene plastic sheeting can be used as a vapor retarder. Some cellulose manufacturers recommend against the use of vapor retarders in walls insulated with spray-applied cellulose. СІМА is not aware of any endemic problems resulting from this practice.7 Research reviewed for this book does not suggest that there is sufficient evidence to eliminate vapor retarders from conventional construction. It is important to note that each building is fairly unique in terms of wall construction, interior use, and environmental conditions, and should be evaluated individually by the building designer. If unsure, the homeowner could consult the local or state building codes about the use of vapor retarders. The insulation manufacturer also may provide recommendations on where to place a vapor retarder.