Flex

Flex pens are a type of writing instrument that provides line variation controlled by the writer. They write a wider line as you press harder - the tines spread and the ink's surface tension bridges the gap created and makes a thicker wetter line.

Flex nibs are easier to spring (damage by bending past the point of spring-back) due to their softness and their being intended for the writer to bend. Titanium nibs are known for providing a different kind of feedback which makes it harder to identify when they are about to spring, making them easier to damage.

Compare to other forms of line variation:

• Stub/italic nib: provides line variation due to its asymmetrical tip (shaped like a rounded rectangle) and so line variation is determined by the angle of rotation.
• Fude nib: bent up at the tip, and provide a thinner line as the pen approaches 90º to the paper.

Dip Nibs

Dip nibs are nibs intended for a nib-holder and dipped in ink. These provide the largest line variation and are disposable, un-tipped, and soft. Depending on your paper, writing pressure, and nib, you will need to change your dip nib with more or less frequency.

Some fountain pens are made to use dip nibs, from companies such as Desiderata, Osprey, and Ackerman. The nibs are similar in size to a #6 fountain pen nib, and there are some tutorials for flattening the nib or modifying the feed to cram a dip-nib such as a Zebra G onto a Jinhao or Noodler's fountain pen.

Fountain Pens

Formerly, many fountain pen makers produced pens that came with flex nibs. These were usually gold tipped with an iridium alloy; in contrast to dip nibs, these are durable/non-disposable, tipped for a smooth writing experience, and had varying levels of softness.

Modern fountain pen manufacturers do not produce a "full flex" nib similar to this, however you do have a few options:

• Use a dip nib, as detailed above. These are un-tipped and will not be a smooth writing experience. But they do provide the most flex.
• Pilot's FA nib is generally regarded as the flexiest production nib available. The feed for these is designed for Japanese calligraphy, which involves shorter strokes than western scripts - so many writing in western scripts have had issues with ink starvation. If you are willing to void your warranty, you can remove the breather tube to increase ink flow.
• Wahl Eversharp has also started producing flex nibs that compare with Pilot's FA. Aurora also came out with a limited edition flex pen in 2017.
• Various other manufacturers do have "soft" nibs. These are not intended to be flexed, but do provide some limited line variation.
• Noodler's and Fountain Pen Revolution produce steel flex nibs. These are intended to be flexed, but require substantially more pressure than vintage pens. The popular ease my flex mod removes some of the nib material to reduce the required pressure.
• Some nibmeisters will add flex to an existing nib.

Why are full flex nibs no longer produced?

Ask a pen manufacturer.

However, some likely reasons are:

• They are easier to spring, so manufacturers would expect more returns/warranty-claims.
• They may be more difficult to produce, so would be more expensive.
• The market for flex may be small.