Light weight and made of long, resilient glass fibers bonded with an acrylic thermosetting binder, the sheets are wrapped in plastic for a cleaner, more comfortable installation with less itching and dust. The plastic facing also serves as a vapor retarder that resists water vapor transmission. (An alternative, non-vapor retarding plastic is also available for hot and humid climates.) ComfortTherm is also noncorrosive and mod-resistant and does not settle, breakdown or sag due to vibration