A method of manufacturing/making mineral fiber (e.g. fiberglass) thermal insulation batt is disclosed wherein a base mineral fiber layer is impregnated with a two-layer layering system so as to produce a batt which is substantially vapor impermeable with a perm vapor rating less than about one. The first layer of the layering system is of a low melt material while the second layer is of a high melt material, the first layer being sandwiched between the base insulating layer and the second layer, and functioning to bond the layering system to the base. In certain embodiments, the first layer includes quick blooming ethyl vinyl acetate (e.g. from about 10-25% by weight) and a low density (e.g. 22-26 lbs. per cubic foot) polyethylene, and the second layer includes high density (e.g. 28-38 lbs. per cubic foot) polyethylene. The resulting insulation batt is vapor impermeable, less susceptible to cold-crack, easier to manufacture, fire retardant, more durable, and easier to handle.