They're very thin nylon picks. They're good for practicing the hand motions of strumming; they put up very little resistance, so they train you to keep your hand stable. I still sometimes play with them since they give a really nice bright tone, but I usually want something thicker in order to be able to flatpick melody lines in between strums. I also sometimes use them when practicing flatpicking, since flatpicking with a really thin pick reveals things about your body mechanics that you don't notice with a thicker pick.