Causes of pen leaks & how to prevent them from happening

a white fountain pen writing on paper

Have you ever wondered why a ballpoint pen can sit happily for years in a drawer or on a desk without leaking but pop it in your pocket, and it offers your clothes an unwanted blue or black splodge within the hour?

How about fountain pens and their alleged misbehaviour in pockets, in bags, and on aeroplanes?

This blog post takes a look at each pen type, separates the myths from the facts, and explains how to avoid any potential leakage issues.

Leaking ballpoint pens

Despite leaking in your pocket, a ballpoint pen won’t lose any ink when it is shaken or dropped.

So, why do they leak in our pockets? There are two big reasons.

The first reason is body heat. As the pen heats up, the ink liquefies, and this allows it to ooze from the tip. The small grease plug in the ink reservoir also liquefies, meaning the ink can potentially flow from both ends of it.

Bear in mind that this could happen in hot weather as well as when the pen is stored on your person.

Secondly, the capillary action that is at the heart of how a ballpoint pen functions means that when the pen makes contact with fabric, the ink gets pulled of the pen and absorbed into the fabric.

This can take place despite and in opposition to the laws of gravity, so will happen at any angle — even if the pen’s nib is pointing upwards in a shirt pocket.

The ink travels particularly well in fabric, unfortunately.

Personally, I carry my ballpoint pen with me in my handbag and have never had any problems with leakage.

However, it is recommended that they are stored vertically (and capped or retracted).

a ballpoint pen leaking in the pocket of a shirt

Leaking rollerball pens

Due to the way they function, the ink in rollerball pens is thinner than that of ballpoint pens. It is often a water-based ink and is more similar to that used in fountain pens than ballpoint pens. This ink, combined with the nib, provides a generally smoother writing experience.

However, because the ink is thinner, it is more likely than a ballpoint pen to leak when exposed to heat.

That being said, though, when stored away from heat, you shouldn’t have any issues.

Store these pens vertically where possible and always cap or retract them.

Leaking fountain pens

Fountain pens have a reputation for being leaky whereas modern versions are much less likely to leak than their earlier counterparts.

In fact, in general use, a functioning fountain pen will not leak. If your fountain pen is leaking, then it requires repair. Do bear in mind though that a little bit of ink on the nib is relatively common and nothing to worry about — this is called ‘nib creep’ and does not affect the functioning of the pen at all.

Fountain pens in flight

an airplane in the sky surrounded by clouds

When travelling by air, issues with fountain pens are possible but are also easily avoidable if you plan ahead.

If you don’t wish to use a pen on the flight, simply flush it before you travel and carry the ink separately. An empty pen cannot leak.

If you do want to write during the journey, completely fill the ink chamber with ink. Most problems occur when the ink chamber is semi-full because the air inside the chamber can expand with additional cabin pressure — forcing ink through the nib. If there’s no space for air to gather in the chamber, this cannot happen.

Make sure you keep the nib upright for take-off and landing. The pressure variation in the cabin is the greatest during this time, and if the nib were pointing downwards, there would be a risk of air pushing additional ink out when you use it. It goes without saying, but keep it capped too.

Once the aeroplane is cruising, you are safe to start writing. Uncap the pen nib end up, just to be on the safe side.

If you are still concerned about your pens during flight, store them in a zip lock bag — whether in your carry-on luggage or your pocket. Then, if the worst happens and your pens leak, the ink will get no further than the plastic bag.

In conclusion, I would recommend storing ballpoint and rollerball pens vertically and in colder environments. When it comes to fountain pens, store them in a cool and dry place at the angle you prefer. However, if you take them on a flight, prepare in advance, and you’ll avoid any leaking issues.

What has been your experiences of leaking pens? Let us know in the comments!

As a long-term stationery lover, I adore working for The Pen Company. My childhood saw me carrying around a little red briefcase covered in stickers and full of pens, paper and other such goodies; my adulthood sees me doing pretty much exactly the same!