Glass is made up of a mixture of silica sand (also known as white sand or quartz sand), soda ash, and limestone. Although these elements are natural and in theory glass can be recycled infinitely, it is not the most sustainable material.  

First of all, it might seem that sand is not a rare substance, yet, today the world is running out of sand, as it is the most consumed resource on earth after freshwater.

Secondly, glass production is highly energy-intensive. Besides, glass is heavy to transport. These factors lead to significant carbon emissions which, in turn, contribute to global warming.

It is true that glass can be recycled, but sometimes it is a difficult process due to its weight compared to other materials, which impacts transport. Additionally, its fragility can cause issues with machinery as well as fears of the contamination of other recyclables (such as paper and card) in single-stream recycling systems.

Unfortunately, not all glass items can be recycled— for example, neither mirrors nor heat-proofed glass can be recycled. Lots of glass end up their life in landfills. But that is a problem, because it takes at least 4,000 years for glass to break down.