STRATHMORE SEQUENTIAL ART SURFACES 500 SERIES BRISTOL - 100% cotton bristol. Plate surface has a ultra smooth finish great for detail work with pens, markers and airbrush. Semi-smooth is slightly textured, suited for pen and ink, pencil and specialty pens. The vellum surface has a tooth, finish excellent for graphite pencil, colored pencil, sketching sticks and specialty pens and markers. Charcoal, pen and ink, airbrushes and light wash also work great with vellum. Acid free.