Shore D scale is for testing the following materials:

Rubber: Hard
Plastics: Harder grades such as rigid thermoplastics, plexiglass, thermoploystrene, vinyl, sheet, cellulose acetate, thermosetting
Laminates (ie Formica)
Other: Paper filled calendar rolls, calendar bowls, etc. (materials that would not normally indent under fingernail pressure, such as a pocket comb or bowling ball).