Sag-resistant fiberboard containing hydrophilic binder

Claim 1

IN A RECTANGULAR UNIT OF FIBERBOARD COMPRISING A POROUS BOARD OF FELTED FIBERS AND HYDRPHILIC BINDER FOR SAID FIBERS, WHICH UNIT HAS AT LEAST TWO OPPOSITE EDGES ADAPTED FOR MOUNTING THE UNIT HORIZONTALLY, AND WHICH IS CHARACTERIZED BY SOFTENING OF THE SAID BINDER AT HIGH HUMIDITY THUS INDUCING SAID UNIT WHEN MOUNTED HORIZONTALLY ONLY AT SAID OPPOSITE EDGES TO SAG, THE IMPROVEMENT IN WHICH FIBERS AND INTER-FIBER BONDS AT AND ADJACENT A SURFACE OF THE UNIT ARE COATED WITH THERMOSET MOISTURE-RESISTANT RESIN FORMING A CONTINUOUS RESINOUS STRUCTURE OVER THE AREA OF SAID SURFACE OF THE UNIT BETWEEN SAID OPPOSITE EDGES, AND IN WHICH SAID RESINOUS STRUCTURE IF FORAMINOUS WITH A MULTIPLICITY OF ISOLATED AREAS IN SAID SURFACE, SAID AREAS CONTAINING FIBERS AND INTER-FIBER BONDS NOT COATED WITH SAID THERMOSET RESIN, WHEREBY SAID ISOLATED AREAS EXHIBIT POROSITY CONTINUOUS WITH THE POROSITY OF THE BODY OF THE UNIT FOR TRANSMITTING THROUGH SAID AREAS SOUND WAVES ENTERING SAID UNIT AT THE OPPOSITE SURFACE.