Abstract: An economical and versatile fibrous glass mat displaying improved resistance to wetting or strike-through by various curable materials when said materials are placed on one surface of said mat while in liquid state is disclosed. This mat, which is especially suited as a carrier, substrate or facer for such curable substances, comprises a blend of fibers. This blend of fibers includes a majority of base fibers having a mean diameter in the range of ten (10) microns with a minor amount of microfibers. The binder formulation, which when cured holds the blend of fibers together to form a self-supporting mat, includes conventional binder resins with a minor amount of wet proofing resinous materials.Preferably, the resulting mat has a porosity of no greater than two-hundred and twenty-five (225) cubic feet per minute per square foot of mat in accordance with the Frazier Air Permeability Test.