a writing, drawing, and drafting instrument in which the writing element is a porous fiber rod, or core, in a plastic body. Inside the body is a feeder element saturated with ink; the writing core is attached to one end of the body, and the other end is capped. The feeder consists of a filter made of porous paper with a packing of cotton or synthetic fibers that form capillaries. Feeders of this type soak up ink efficiently and feed it easily to the writing core. Special water-base inks are used; they do not clog the capillaries of the feeder and the writing core but flow freely through the instrument. Soft-tip pens can write on paper, cardboard, wood, glass, metal, leather, fabrics, and polymer films. The pens are produced in more than 14 colors.
The writing cores of soft-tip pens are made of polyethylene terephthalate (Lavsan), polytetrafluoroethylene (Teflon), and other materials. Teflon cores are more dependable in use than those made of Lavsan, as their tip is only slightly deformed during the writing process. There are also soft-tip pens with porcelain and felt cores. The thickness of the writing core usually ranges from a fraction of a millimeter to several millimeters. In most models the feeder is filled with ink only once, at the time of manufacture. In some reuseable models the ink can be replenished as it is used up; other models have removable ink cartridges (feeder and core) that can be replaced when the ink in the original feeder is exhausted.
A. P. TSVETKOV