Methods of making gypsum panels, fiberglass mats, and associated gypsum panels and building sheathing systems are provided. In one aspect, a method of making a gypsum panel includes depositing an aqueous liquid containing a wetting agent onto a fiberglass mat, such that the aqueous liquid penetrates an entire thickness of the fiberglass mat, and depositing a gypsum slurry onto the fiberglass mat onto which the aqueous liquid has been deposited, such that the gypsum slurry penetrates at least a portion of the fiberglass mat. In another aspect, a method of making a gypsum panel includes depositing an aqueous liquid containing a wetting agent onto a fiberglass mat, and depositing a gypsum slurry onto the fiberglass mat onto which the aqueous liquid has been deposited, prior to drying of the aqueous liquid, such that the gypsum slurry penetrates at least a portion of the fiberglass mat.