What Is Glass?
Glass is a hard substance created by melting silica, which is derived from sand, and adding compounds such as soda ash and limestone. It is commonly found in drinkware, containers, vases, decor, windows, and mirrors.
There are four types of glass typically found in the home.
- Soda-lime glass – Most glass falls under this category, which is less expensive to manufacture and is adequate for daily use. However, this type of glass is more prone to cracking or breaking under sudden temperature changes.
- Tempered glass – This is soda-lime glass that has been treated with heat or chemicals to make it 4-5 times stronger than regular glass in terms of impact resistance, and more resistant to thermal shock. Pyrex is a well-known example of this type of glassware.
- Borosilicate glass – A specialized type of glass containing boron trioxide (stable and harmless in glassware), which makes it the most thermal shock-resistant type of glass. It is typically more expensive than soda-lime glass and found in high-end drinkware and bakeware.
- Crystal glass – Known for its beauty, crystal glass contains elements such as zinc or barium to improve its shine. Its hardness depends on the metal additive and manufacturing process, but overall, crystal is not as hard as other types of glass; this allows for intricate etchings and designs.
How Glass Is Made
Glass manufacturing process can be divided into four main steps: batching, melting, forming, and finishing.
- Batching – During this first stage, sand, soda ash, lime, and other components are measured to the exact proportions for the desired color, weight, or thermal performance of the finished product, and then thoroughly mixed.
- Melting – The mixture is heated to approximately 1500°C (2732°F); this stage accounts for about 75% of total energy consumption throughout the production process.
- Forming – As the glass mixture cools, it becomes an amorphous solid with a texture similar to warm honey. It is poured into one of four different forms that glass is classified into: flat, container, specialty glass, or fiberglass.
- Finishing – The final finishing process varies to determine the specific characteristics for the final product.
Toxicity and Safety
All types of glass are exceptionally safe materials because their surfaces are non-porous and generally do not leach chemicals. However, there are two heavy metals that you should be cautious of:
- Lead – Caution should be used with vintage or crystal glassware, as well as imported products, which may contain significant amounts of lead. Vintage pieces often contain lead, which was added to achieve their sheen, and determining whether pieces contain lead can be difficult.
- Cadmium – Sometimes used in decorative paints or glazes on glassware, particularly in older or imported items.
Neither of these elements is safe in any amount, so ensure products are labeled as lead- and cadmium-free.
Sustainability of Glass
Glass is arguably one of the most eco-friendly materials when reused or recycled, but when it isn’t, things get much more complicated. It remains a safe and inert material, even through its end-of-life, but when not recycled, the significant drawbacks related to sourcing, energy use, and transportation emissions become more prominent.
Sourcing
According to the UN Environment Programme (UNEP), “the extraction, sourcing, use, and management remain largely ungoverned in many regions of the world, leading to numerous environmental and social consequences that have been mostly overlooked.” Sand may be abundant, but its extraction can damage ecosystems, harm biodiversity, increase erosion, and affect groundwater. Labor exploitation within this industry is also of concern. Granted, the vast majority of extracted sand is used in concrete, but it is important to be aware of these impacts nonetheless.
Production
Glass production is an energy-intensive industry, primarily due to the extremely high temperatures needed to melt raw materials for glass formation, which are much higher than those needed for plastic or aluminum. Three-quarters of the energy used to produce glass is consumed during the melting phase, and most of this energy (75%) comes from natural gas furnaces, while the remainder comes from electrically powered furnaces.
Transportation
Because glass is significantly heavier and requires more space than plastic or aluminum, its transportation requires more fuel, thereby resulting in higher greenhouse gas emissions. Heavier and bulkier packaging may also be required to prevent breakage, adding to the weight and reducing space efficiency.
End of Life
Unless bumped or dropped, glass is durable and can be used and reused indefinitely.
Basic soda-lime glass is infinitely recyclable with no loss in quality. When recycled, glass is crushed into small pieces called cullet, which require lower temperatures to melt than raw materials used to make new glass, using up to 40% less energy.
Crystal, borosilicate, and tempered glass are another story when it comes to recycling. Since the first contains metal alloys, it cannot be mixed with standard soda-lime glass. Nor can the latter two types, due to their higher melting points. These may technically be recyclable, but finding specialty recyclers is a tall order, and I am not aware of any companies that offer recycling of their products (Pyrex does not). You can always check with specific manufacturers.
While glass is not biodegradable, it is made from silica (the most prevalent element in the Earth’s crust), is chemically inert, and does not leach harmful chemicals when disposed of.
Learn more about glass recycling here.
Should You Choose Glass?
Because of its non-toxic, reusable, and recyclable qualities, glass is an excellent material to use. From a health and safety standpoint, it is among the best options. For sustainability, it is a much more difficult question to answer. If a glass item is utilized as a single-use product and not recycled, its high carbon footprint drastically reduces its eco-friendliness. Still, despite the high energy use in production and transportation, and even when sitting in a landfill, glass offers important advantages: it is derived from natural elements rather than fossil fuels, does not contain harmful chemicals, does not shed microplastics, and remains chemically inert throughout its lifecycle. For me personally, the toxic chemicals in plastic and microplastic particles have led me to choose glass over plastic every time.
Best Uses for Glass: Anywhere in the kitchen, including food storage containers, drinking glasses, and bakeware. Household cleaning spray bottles, skincare and cosmetic packaging
Compare glass with other common materials such as aluminum, stainless steel, plastic, silicone, and ceramic.
| Pros of Glass | Cons of Glass |
|---|---|
| Very safe; does not leach chemicals or microplastics | Can crack, chip, or shatter if mishandled |
| Durable and long-lasting when properly cared for | Heavy and less portable than other materials |
| Does not absorb flavors, odors, or stains | More expensive than other materials, such as plastic |
| Reusable for many years | May have overall higher carbon footprint than other materials |
| Transparent, allowing you to see contents | Production is energy-intensive |
| Some forms are very heat-resistant | Transportation has a larger carbon footprint due to weight |
| Made primarily from naturally occurring materials (sand, soda ash, limestone) | May not be suitable for some outdoor or high-impact uses |
| Widely recyclable and can be recycled indefinitely without loss of quality | Recycling availability varies by location |
Sources:
Li, R. (2019, October 31). How Glass is Made: A Step-By-Step Process. Roetell. https://www.roetell.com/how-is-glass-made-a-step-by-step-process/
Miserocchi, L., et al. (2024, October). Status and prospects of energy efficiency in the glass industry: Measuring, assessing and improving energy performance. Science Direct. https://www.sciencedirect.com/science/article/pii/S2590174524001983
Why Recycle Glass? Momentum Recycling. https://utah.momentumrecycling.com/why-recycle-glass/
United Nations Environmental Programme (UNEP). (2022). Sand and Sustainability: 10 Strategic Recommendations to Avert a Crisis. https://www.unep.org/resources/report/sand-and-sustainability-10-strategic-recommendations-avert-crisis
U.S. Energy Information Administration. (2013, August 21). Glass Manufacturing is an energy-intensive industry mainly powered by natural gas. EIA. https://www.eia.gov/todayinenergy/detail.php?id=12631