Stopper Fluid: Transparent Liquid In A Pen Lead

Pen ink lead has a transparent liquid inside. But what is that? And what is it for? Let me introduce the role of that stopper fluid.

What Is Stopper Fluid Made Of?

The stopper fluid is made of silicone, silicone grease, liquid paraffin, silicone oil, or vaseline. Silicone, silicone oil, and vaseline are familiarly used in daily products. So, there seems to be no problem in safety even when the ink reverse fluid adheres to the skin.

The Role Of Stopper Fluid

pen lead with stopper fluid

Role 1: Prevent ink leak

The transparent part of the ink was initially created in Japan in 1994 and has been officially patented.

The role of this transparent part (stopper fluid) is to prevent the ink from flowing backwards and leaking.

If it is oil-based ink, it is highly viscous and slippery in the first place. So the ink will not likely leak even if there is no stopper fluid.

However, with thicker ink tubes, the ink seems to flow back and leak when the lead gets damaged or shaken or when the temperature is high.

To prevent this, an ink backflow prevention material is injected into the ink tube. And thanks to that part, we can avoid ink sticking to your clothes and hands.

Role 2: Stop ink evaporation

Water-based inks are less viscous and seem to evaporate more quickly than oil-based inks.

Therefore, in the case of a ballpoint pen with water-based ink, the ink will evaporate from the back end of the pen lead, regardless of the thickness of the ink tube.

If the ink evaporates, the ink will dry out. To avoid that, the stopper fluid is used.

Is Stopper Fluid Edible?

Many people try to move ink by sucking it out of a pen lead when the ink gets separated or clogged.

It is true that if you suck on top of a pen lead and inhale it, the ink will go up. But please don’t do this.

The manufacturer does not use ingredients that are immediately poisonous in the mouth, for example, in case a child accidentally ingests them. But the components of this transparent liquid are said to be silicone, mineral oil, paraffin, and gelling agents.

Since it is not a healthy ingredient, it is best to avoid moving the ink by inhaling it, at the risk of accidentally ingesting it.


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