A vapor retarder is any material that limits the transmission of water vapor. If you're using unfaced fiber glass insulation, a suitable vapor retarder is a 2-mil nylon film called MemBrain™, the Smart Vapor Retarder. Or, you can buy faced fiber glass insulation, which has the vapor retarder already attached. Types of faced insulation include:
- DryRight™ - fiber glass batts with MemBrain, the Smart Vapor Retarder attached.
- Kraft-Faced - kraft paper coated with an asphalt adhesive.
- Foil-Faced - foil-backed paper coated with asphalt adhesive.
- Flame-Resistant Foil-Faced - foil-scrim-kraft (FSK) paper that is strong and resistant to flame spread.