Glass does not flow once it reaches room temperature. The myth that glass flows over time has been perpetuated for years. You may have heard from your high school science teacher that the glass in an old stained glass window thickens at the bottom because it has “flowed down” over time. The glass in these windows is, in fact, often of varying thickness, but that is because of how the sheets of glass were made. There are many glass objects thousands of years older than those windows that show no sign of flow.