The ornamental design for grille cover material, as shown and descirbed.
FIG. 1 is a top plan view of a grille cover material showing our new
design, it being understood that the broken lines depict the boundaries
for the repeat unit of the design and further that the design may continue
in one or more directions;
FIG. 2 is a partial front elevational view of the grille cover material
designated by directional arrow 2 in FIG. 1; and,
FIG. 3 is a partial side view of the grille cover material designated by
directional arrow 3 in FIG. 1.
It will be understood that the broken line showing in FIGS. 2 and 3 is for
illustrative purposes only and forms no part of the claimed design.