This safety feature became standard after international safety regulations , such as those from the International Organization for Standardization (ISO) , required that pen caps be either:
Too large to swallow
Ventilated (with a hole)
Or made of a soluble material
Today, many pen manufacturers follow ISO 11540 , which specifies that pen caps must allow a minimum airflow of 8 liters per minute through the hole — enough to sustain breathing in an emergency.
Fact: In the 1990s, a tragic incident involving a teenager who choked on a pen cap led to widespread adoption of this safety standard.
2. Pressure Equalization: Keeping Ink Flowing Smoothly
Have you ever uncapped a pen and found ink leaking out — or worse, dried up inside?
The hole helps prevent this by equalizing air pressure inside the pen. When a pen is capped, changes in temperature, altitude, or humidity can create pressure differences between the inside and outside of the barrel.
Without a way for air to escape or enter:
Pressure can build up and force ink to leak
A vacuum can form, making it harder for ink to flow
The tiny hole acts as a pressure release valve , allowing air to move in and out gently. This keeps the ink reservoir stable and ensures a smooth, consistent writing experience — whether you’re at sea level or on a high-altitude flight.
3. Manufacturing and Cost Efficiency
From a production standpoint, the hole isn’t just functional — it’s economical .
During the injection molding process , molten plastic is injected into a mold to form the cap. The hole:
Reduces the amount of plastic needed
Speeds up cooling time
Makes it easier to eject the cap from the mold
This translates to:
Lower material costs
Faster production
Less waste
In an industry where millions of pens are made daily , even a tiny reduction in plastic per cap adds up to massive savings.
SEE NEXT PAGE
ADVERTISEMENT
