Instant facts- Just add water 41

Why is there a hole in the barrel of BIC® Cristal® pens?

To equalize the pressure inside the pen with the pressure outside the pen. These vents, or holes in the pen barrels, basically help to prevent ink leakage. Approximately 90 percent of all pens are vented to prevent leakage. The pens that do not have vented barrels contain sealed ink systems and are pressurized.
in www.bicworld.com