A flooring installation is characterized by installing an underlayment between the flooring material and the subfloor. The underlayment includes (from the subfloor up) a foamed polymeric layer and a glass fiber mat. The foamed polymer interpenetrates at least the lower portion of the glass mat. The upper portion of the glass fiber mat is preferably unsaturated. The glass mat may have an acrylic latex tie coat opposite the foamed polymer layer.
