Foam insulation has been installed in the walls. The foam provides an airtight barrier to the exterior of the home to reduce air infiltration and provides a very effective air and acoustic seal around electrical boxes, plumbing pipes and plate penetrations. The foam additionally reduces noise levels created by the "echo" effect of the plumbing and water system throughout the home.  Foam is also applied under all bath tubs, which is a potentially large air leakage area.  This effectively seals this area and provides additional comfort by keeping tub water hot for a longer period.