The ornamental design for a sheetmaterial, as shown and described.
FIG. 1 is a front view of a sheet material according to the design; and,
FIG. 2 is an enlarged detail view of area 2 circumscribed within FIG. 1.
The broken line perimeter of the drawing depicts the boundaries of the claim and forms no part thereof. The dot dash dot broken lines within FIG. 1 and around FIG. 2 denote the boundaries of the detail area and form no part of the claimed design.