Environmental impact of glass | How Sustainable is Glass?

Published on: September 13, 2020

Is glass environmentally sustainable?

Okay, I know you want a simple answer to whether glass is really sustainable, but the answer is much more complicated than just saying “Yes! Because it’s infinitely recyclable”.  In this post, we’re talking about:

  • How glass is made
  • Why we need to consider the sustainability of the raw materials used to make glass
  • How much recycling helps shrink the carbon footprint of glass manufacture
  • How much recycling improves the environmental impact of glass manufacture

Let’s jump right into it.

How are glass containers made?

Sand is required to make glass.  Glass is made up of a mixture of silica sand (also known as white sand or quartz sand), soda ash, and limestone.  These virgin materials are heated to molten, which requires temperatures of between 1400-1600 °C (about 2550-2900 °F).  The molten mixture is then cut and shaped through a couple different processes. 

Colored glass is made by adding different minerals to the sand, soda ash, limestone mix:

  • Green glass: iron, chromium, and copper
  • Blue glass: cobalt oxide and copper
  • Black glass: can be made by adding a high amount of iron to the mixture or adding iron mixed with copper and magnesium oxide

Glass has to be separated into different colors at recycle centers before it can be truly recycled (i.e. blue glass can’t be recycled to make a colorless bottle or even an amber or brown bottle).

Frosted glass is achieved by sandblasting clear glass (regardless of color).

How much does recycling glass help reduce carbon emissions?

Mixing in crushed recycled glass, known as cullet, helps those raw materials, silica sand, soda ash, and limestone melt faster.  Why?  Because cullet has a lower melting point than each of those raw materials. 

a hand holding glass cullet pieces
What cullet looks like - ground up pieces of glass

Do you know why they spray magnesium chloride on roads in winter in cold parts of the country?  Magnesium chloride dissolves in the water on the road ways lowering the melting point of water creating a slushy mix instead of black ice.

Since cullet glass is a solid mixture of silica, soda ash, and limestone, the cullet melts at a lower temperature than virgin glass materials.  When recycled glass cullet is mixed in with raw materials to manufacture glass, the melting point drops from between 2550 to 2900 °F to between 2250 and 2350 °F, which is a huge energy savings.

Glass cullet can be mixed in with virgin raw materials at up to 60% of the mixture.

Using recycled glass (cullet) in the glass making process reduces the energy required during glass manufacturing by about 30%

How much does recycling glass reduce the environmental impact of resourcing raw materials for glass manufacture?

Did you know that the world is running out of sand, and sand is the most consumed resource on earth after freshwater

Sand used to make glass is pulled from sand dunes (a large sand mining operation lies along the banks of Lake Michigan and ranks as the third largest in US industrial sand production).

sand mining and sand excavation to meet the world's demand for sand

A number of illegal sand mining operations threaten ecosystems, and believe it or not, illegal sand mining has resulted in murder on several continents.  The demand for sand is so high, sand mafias have formed in parts of India and Kenya.

Sand is being stripped from floodplains making flooding more of a reality in regions where this illegal mining is taking place.  It’s also being stripped from riverbeds and beaches.  Dredging sand from riverbeds can disrupt ecosystems and kill fish.

In 2013, glass manufacture accounted for about 42% of the global demand for sand.  Sand is also needed for concrete – for roads, for urbanization, to add land mass to support growing populations like in Singapore.  Sand is also used in silicon chips in smart devices and in computers.

As for glass manufacture - While glass is infinitely recyclable, new raw materials have to be used in each batch (at least 40% virgin materials), which means that even though recyclability is high, raw materials are still being used with every batch of glass made.

Plus, recycled glass doesn’t always go into making new glass containers. 

Recycled glass is also used for concrete (so is sand), fiberglass, glass wool, lightbulbs (I know you know this, but it’s one I don’t regularly remember), ceramics, and as an ingredient in the reflective paint on roadways.

Other considerations

Glass is HEAVY.  A 4 ounce glass bottle is about 4 times heavier than a 4 ounce plastic bottle.  This means the carbon footprint due to shipping glass is more significant than for a plastic bottle.

How to reduce your environmental impact when it comes to glass consumption

  1. REUSE FIRST, and if you can't reuse, RECYCLE! 
  2. If you can find the same item in 100% recycled aluminum can instead (or in a paper carton), opt for those instead of glass.  Both are more sustainable than glass.
  3. It sounds weird, but colorless glass is more flexibly recycled.  It's not possible to use one color of glass container to make a different color glass container in the future, but the exception is colorless glass, so opt for colorless if you have a choice.  If you don't have a choice, select products packaged in more "normal" glass container colors (like the color of wine bottles or standard blue glass).
  4. Buy as locally made as possible.  If you live in California, buy a California wine instead of an Italian wine because that bottle didn't have to travel as far to reach you, and carbon emissions due to shipping are real (I've got an upcoming post dedicated to that topic).
  5. Consider alternatives to cement.  Yeah, you read that right.  If you're building a patio or anything else and you were thinking about using cement, consider other alternatives that don't use sand.  Not only does cement use sand, it's also a major greenhouse gas emitter and accounts for between 5% and 10% of global greenhouse gas emission (GHG emissions).
  6. Consider alternatives to concrete (see #5).
  7. Keep your cell phone longer and your computer longer still, and seriously consider whether you need to purchase a new smart device before pulling out that credit card.  Since silica sand is needed for the silicon chips in smart devices, this is one way you can cut down on your use of sand.

Stay tuned for the next post in this series where we talk about plastics.  And, if you liked this article, be sure to sign up for Rain Organica's newsletter where we share more tips about sustainable practices you can easily incorporate to reduce your environmental footprint.

Brandy Searcy founder Rain Organica

About the Author

Brandy Searcy is an outdoor girl who loves hiking, gardening, bird-watching, and body boarding.  Her innate curiosity means she's constantly researching something, and she's likely sharing what she's learned here on the blog. 

Nearly obsessive about her skincare, she started developing products to pack with her on day hikes and soon realized her backpacking friends were searching for a portable skincare routine as well, and that's how Rain Organica started.

Brandy's LinkedIn Bio

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