The Pigma Micron is a long-lasting marker pen (non-refillable) with a hard fiber point suitable for writing or drawing. The pigmented ink in these pens is permanent, lightfast, waterproof and fast-drying. It will not bleed on most artists' papers. These pens are highly useful for studio or field work, and work especially well for drawings which will receive watercolor washes. The 6-pen black ink set comes with .005, .01, .02, .03, .05 and .08 nibs for achieving a wide variety of lines.