1.1 ,This practice outlines factors to be considered, describes design principles and procedures for water vapor retarder selection, and defines water vapor transmission values appropriate for established criteria. It is intended for the guidance of design engineers in preparing vapor retarder application specifications for control of water vapor flow through thermal insulation. It covers commercial and residential building construction and industrial applications in the service temperature range from ,−,40 to ,+150°,F (−,40 to ,+66°,C). Emphasis is placed on the control of moisture penetration by choice of the most suitable components of the system.