I claim the ornamental design for an upholstery material, as shown and described.
FIG. 1 is a perspective view of an upholstery material, showing my new design;
FIG. 2 is a front elevational view of FIG. 1, the rear elevational view, left-side elevational view, and right-side elevational view all being a mirror image thereof;
FIG. 3 is a top plan view of FIG. 1; and,
FIG. 4 is a bottom plan view of FIG. 1.
The upholstery material is shown with a symbolic break in its length and width. The appearance of any portion of the article between the break lines forms no part of the claimed design.