Underlayment provides floor isolation to prevent sound transmission, structural noise transmission and impact noise.Floor underlayment is constructed of a flexible non-lead loaded solid mass barrier fusion-bonded to a ¼" 8-10 lbs. density closed-celled PVC foam decoupler. The foam layer of this carpet underlayment decouples the layers of floor materials to prevent floor vibrations from transmitting structural or airborne sounds from noise sources.