A gypsum board having glass fiber reinforcement. The glass fiber has sizing promoting bonding with a gypsum matrix. The glass fibers are added to the gypsum matrix cia a non-woven glass fiber mat bonded initially with a dissolvable or reversible binder to maintain the three dimensional architecture of the non-woven glass fiber mat during handling and insertion into a cast wet gypsum slurry forming a gypsum board. Upon insertion in the wet gypsum slurry, the dissolvable bond between the glass fibers in the non-woven glass fiber mat dissolves and allows the sizing coating on the glass fibers to make intimate contact with the gypsum matrix. In case of the reversible bond, the bond adhesive hydrolyzes during the gypsum board drying cycle providing intimate contact between the sizing coated glass fibers and the gypsum matrix. The non-woven glass fiber mats bonded to the gypsum matrix provides improved strength and flexure resistance of the gypsum board.