Weather Resistive Barriers Weather resistive barriers are part of an exterior wall system designed to protect building materials from moisture penetration. There are different types of weather resistive barriers including vapor barriers, vapor retarders, air barriers and air retarders. Not all air barriers are vapor barriers and not all vapor barriers are air barriers, however, all weather resistant barrier membranes must resist entry of liquid water (rain/snow) into the wall system by providing a drainage plane. There are three general classes of membranes based on permeability. CLASS
MEMBRANE TYPE
VAPOR PERMEANCE
Class 1
Vapor Barriers
1 perm or less
Class II
Vapor Retarders/Semi Permeable
More than 1 perm and less than 10 perms
Class III
Breathable
10 perms or more
| WrapShield | Fiber Image | Construction | Water Vapor Transmission | Air Permeability |
| Weather resistant vapor permeable air barrier membrane |
 |
Triple layer spunbond polypropylene | 308.9 grams/m2/24hrs 50 perms |
0.0019 cmf/ft2 0.0095 L/s/m2 |
| WallShield | Fiber Image | Construction | Water Vapor Transmission | Air Permeability |
| Weather resistant vapor and air permeable breather membrane |
 |
Triple layer spunbond polypropylene | 576 grams/m2/24hrs 212 perms |
Not an air barrier, but has been tested as a component in a composite air barrier tested assembly |