why does glass coffee makes not break

Why Does Glass Coffee Mugs Not Break

Most people have enjoyed coffee from a glass mug at some point. Glass mugs come in a variety of styles, from the very simple to the very ornate. But did you ever wonder why glass mugs for coffee don’t break when filled with hot coffee?

Making Glass Stronger

Glass is a brittle material and is easily broken. To make glass strong enough for coffee mugs, manufacturers must add other elements to the mix when making the glass. Here’s what they do to make glass mugs stronger:

  • Adding Boron Oxide – Boron Oxide is added to the melted silica glass during production. Boron Oxide can change the strength of glass significantly, making it more heat resistant and less likely to shatter.
  • Tempering and Annealing – The glass mug is then heated and cooled rapidly. This process is called “tempering” and makes the glass more durable. The process of “annealing” is then used to cool the glass slowly. This relieves any stresses that were created during the tempering process to further reduce the chances of breaking.
  • Adding Lead – Lead is also used to make glass stronger and more heat-resistant. Lead also helps give glass its clarity and brilliance.


Glass coffee mugs are made to be heat-resistant and break-resistant thanks to the added ingredients during the production process. In addition to these elements, many glass mugs are double walled to insulate the coffee, which also helps prevent them from breaking. Even with all these precautions, it’s always a good idea to handle glass mugs with care, as glass can still break when dropped.

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