D'Addario Classic Celluloid Thumb picks Size : Medium , LargeCelluloid is one of the most popular guitar pick materials today. It's available in a wide variety of shapes, colors, and thicknesses, and provides a natural feel and warm, fat tone. A man-made material, celluloid was first introduced in the early 1900s as a substitute for natural tortoise shell picks.IDEAL FOR: ACOUSTIC GUITAR / BANJO