8.0 What is a true "flex" nib?

When a nib has "flex", it means that the tines of the nib will tend to move outward when pressure is applied while the pen writes. This causes the space between the tines to widen and thus lay down more ink, causing the line width of the pen to vary based on the pressure applied to the nib. Hence, flex nibs are wonderful at adding expressiveness to the actual writing being done.

Nibs which are "springy" have a certain amount of "bounce", but the tines do not flex outward when downward pressure is applied.

The Namiki Falcon is a good example of a modern "flex" nib. I also own Eversharp Skylines with flex nibs, as well as a Waterman 52 (which is pretty close to a "wet noodle").