The UM-151 is known for its smooth writing, exceptional ink quality, and outstanding selection of colors and tip sizes. Find the perfect one for any task, whether it's writing meticulous notes, arking your calendar, or decorating your scrapbook with colorful captions. The sturdy tip does not bend or break, even with heavy-handed use. The pigment-based ink flows smoothly and is waterproof, fade-resistant, and feather-resistant. Much of this great performance is due to the special viscous properties of the ink. As the ink passes through the pen tip during writing, the viscosity drops to provide smooth ink flow.