What is a Flex Nib?

Flex nib (or flexible nib) is a type of fountain pen nib that can create different line widths. Due to its non-rigid structure, a flex nib allows a writer to control line width by adjusting the pressure of the pen on paper. Increased pressure will cause the two tines of the nib to separate slightly, allowing more ink to flow onto the page. A lighter grip will allow the tines to remain close together and produce a thinner line.