Micron Pigma Pens contain pure black pigment in a felt tip! Waterproof and chemical proof. They are excellent for drawing, graphics, documents, outlining and lettering work. For best results spray with a matte varnish after using so that the ink won't smear (it may if varnish is brushed on). The larger the number the thicker the line. Note: When not using these pens ensure that the cap is on tight. These pens have a felt tip so remember not to press too hard or the tip may bend causing ink flow to stop. This set contains three sizes of tips: .01, .03 and .05.