Why Does the Coffee Cup Lid Have a Tiny Second Hole? Know the Science Behind It

What is the purpose of the small second hole in the coffee cup lid? Learn About the Science Underlying It. (Pics: Freepik)
Gayatri Hasabnis
By : Published: 26 Feb 2026 00:20:AM
Every one of us love drinking coffee but have you observed that the coffee cup lid has a tiny second hole? There is a science behind it.

Every one of us love drinking coffee but have you observed that the coffee cup lid has a tiny second hole? There is a science behind it.

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By allowing air in as you drink, the little second hole on the cover of a coffee cup, sometimes referred to as a pressure equalization port, prevents a vacuum and guarantees a smooth, splash free flow.

By allowing air in as you drink, the little second hole on the cover of a coffee cup, sometimes referred to as a pressure equalization port, prevents a vacuum and guarantees a smooth, splash free flow.

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Additionally, it enables steam to exit, which helps to maintain a tight cover and prevents pressure from building up. The explanation for this is straightforward. The creation and delivery of food is also backed by science.

Additionally, it enables steam to exit, which helps to maintain a tight cover and prevents pressure from building up. The explanation for this is straightforward. The creation and delivery of food is also backed by science.

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Your mouth forms a seal when you drink from the main hole. A vacuum will develop if the liquid leaves and there is no air to take its place, which will cause the coffee to glug or gush out unexpectedly.

Your mouth forms a seal when you drink from the main hole. A vacuum will develop if the liquid leaves and there is no air to take its place, which will cause the coffee to glug or gush out unexpectedly.

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Steam is produced by hot coffee. This steam is released through the tiny, typically elevated hole, which keeps the cover from blowing off due to increasing pressure. (Disclaimer: Given the input is on an information basis, please seek professional advice.)

Steam is produced by hot coffee. This steam is released through the tiny, typically elevated hole, which keeps the cover from blowing off due to increasing pressure. (Disclaimer: Given the input is on an information basis, please seek professional advice.)

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