A marker, or felt-tip pen, has a porous tip of fibrous material. The smallest, finest-tipped markers are used for writing on paper. Medium-tip markers are often used by children for coloring. Larger markers are used for writing on other surfaces such as corrugated boxes,whiteboards and for chalkboards, often called "liquid chalk" or "chalkboard markers." Markers with wide tips and bright but transparent ink, calledhighlighters, are used to mark existing text. Markers designed for children or for temporary writing (as with a whiteboard or overhead projector) typically use non-permanent inks. Large markers used to label shipping cases or other packages are usually permanent markers.