In this guide, we outline whether metal is more sustainable than plastic, and vice versa.
We compare some of the key factors involved in the production, usage and waste management of each.
Summary – Is Metal More Sustainable Than Plastic?
Breaking Down Which Might Be More Sustainable
Whether metal is more sustainable than plastic depends on the type of metal that is being compared with plastic i.e. whether it’s aluminum, stainless steel, or something else.
It also depends on the item or product in question, how it’s made, and other factors/variables.
But, some general sustainability considerations might be:
1. Sourcing Materials
Both metal and plastic are mined from non renewable resources, but, common metals tend to be fairly abundant.
For example, bauxite used for aluminum generally isn’t considered scarce.
On the other hand, some may question whether we will run out of fossil fuels like oil or natural gas (used as a feedstock for plastic) anytime soon.
Additionally, several commonly used metals tend to have a far higher recycling rate than plastic and can be continuously recycled
What this means is that metals that use recycled material can contribute to a more circular economy – for example, some reports indicate that 75% of all aluminum ever produced is still in productive use
Aluminum cans are an example of a product that may be able to be recycled over and over
Some metals that use recycled material still use virgin material though – some reports indicate that stainless steel might use 60% recycled content, and 40% new/raw content
Metals tend to have a higher production footprint than plastic when considering energy consumption
Some metals consume a significant amount of energy during production, with aluminum reported as being one of the most energy intensive industries
Higher energy consumption can generally mean a higher carbon emissions as a result
But, carbon footprint may depend on the energy sources used, as some reports indicate that a reasonable amount of aluminum is produced using hydroelectric energy.
Hydro energy sources may be more clean than fossil fuels energy sources
3. Transport & Delivery
Plastic tend to be a lighter material than most materials, and might have a lower delivery/transport/freight footprint than some heavier metals
Some reports indicate that amongst metals, aluminum might consume less energy during transport than steel
4. Waste Management & Recycling
Metals can be recycled an infinite amount of times, and some metals have a far higher recycling rate than most plastics (which some say justifies the higher production footprint and energy use).
Once plastic can’t be recycled anymore, it has to be downcycled, sent to landfill, or incinerated.
In relation to some metals though, particularly the ones that are made with alloys, there may be chemicals like chlorine required to break them down
The comments we made elsewhere in this guide about stainless steel and aluminum recycling, and the requirement for virgin material, or being closed loop, also apply here
Read more about the recycling of metal in this guide
5. Pollution, & Impact On Humans, Animals & The Environment
The littering of plastic, and the impact plastic might have on human health, wild life, and the environment, may create more issues than what metal does at the end of it’s lifecycle
Plastic can pollute the land, rivers and lakes, and the ocean, can contain additives and chemicals like BPA that may be a concern for humans (although metal drink bottles can contain chemicals that can leach as well), can be ingested by or entangle wild life, and may create other potential issues in the ocean, and in rivers and on land.
Micro plastics are also released from plastic when it breaks down.
Overall, as a material, plastic has a range of uses, and provides a number of benefits to society. It may have a lower footprint at the production and transport stages than some other materials
But, metal might be more abundant, recycled at a higher rate, and may not contribute to the range of pollution issues that plastic might.
Metal may be a material that can contribute to a circular economy better in some ways than plastic.
But, there’s ultimately many variables in trying to assess each material in a definitive way.
The product in question, the life cycle stage in question, the sustainability indicator being measured, and others factors can all influence which one is more sustainable.
Consumer behavior can also come into the equation (such as how the material or product is used, and also disposed of)
Specifically with drink bottles, a metal bottle like stainless steel or aluminum that is re-used hundreds of times might be more sustainable in some ways than a single use plastic bottle
Examples Of Products With Both Metal & Plastic Options
– Furniture (tables, chairs, beds, etc.)
– Food & Beverage Goods (drink bottles, food containers and lunch boxes, etc.)
– Building/Construction Materials
Metal vs Plastic: Comparison
General Sustainability Of Each Material
– Sourcing Of Materials
The sourcing of metal and plastic requires mining of metal ores and fossil fuels.
Common metal ores are generally abundant, whilst there is debate over the scarcity of fossil fuels
Fossil fuels are also considered non renewable
Something to note though is that metal tends to have a far higher recycling rate in several countries.
Recycled material can be used in new products as opposed to using material from virgin resources only
Some say this is a positive to meet the demand for metal in the future, however, heavy reliance on recycled aluminum in the future may not come without issues, even for meeting demand.
Steel and plastic both consume energy and resources at the production stage
Some metals may use much more energy than plastic during production (some metal industries might be some of the most energy intensive industries in the world when adding up all stages of metal refining and production)
Even though plastic production has some drawbacks from a sustainability perspective, when compared to the production of tin and aluminum containers, it only uses a fraction of the energy … When the production process for each is compared it is found that 1 kg of Polyethylene plastics produce around 4 kg CO2 and 1 kg aluminum produces 10.63 kg CO2 (desjardin.fr)
Using recycled metal material can reduce the sourcing and production footprint of metal products to varying degrees, and may also decrease carbon emissions.
It is estimated that ‘[when metals like aluminum and tin are recycled] … the amount of CO2 created in the production process is only 1/3 of what it would be if new ore were being continually extracted’ (desjardin.fr).
Other estimates indicate that ‘through the recycling process it saves 95% of the energy that it would cost to produce new aluminum’ (azahner.com).
– Delivery & Transport
Some metals are heavier than plastic, so, these metals may have a higher delivery/transport footprint from increased fuel use.
Plastic may also be more space efficient than some metals because of it’s packing or storage properties, and it’s flexibility.
Comparing metals to metals, we can look at aluminum’s energy consumption compared to steel: ‘Aluminum has [a] 20 percent smaller life cycle energy consumption than steel in transportation’ (aluminum.org)
Metal can be more durable than some soft plastics, adding to the lifecycle duration of metal products.
Having said that, some plastics last for decades when in use, with some construction plastics being just one example of this.
Hard plastics like hard plastic drink bottles can also last a reasonably amount of time.
– Waste Management & Recycling
Some metals have a far higher recycling rate than plastic.
For example …
‘… steel produced by predominantly scrap-fed electric-arc furnaces accounted for more than 60% of the total raw steel produced in the United States in 2013’ (theguardian.com)
‘More steel is recycled each year than aluminum, paper, glass and plastic combined’ (azahner.com)
‘By volume, copper is the third most recycled metal following steel and aluminum’ (azahner.com).
Additionally, metal can be recycled an infinite amount of times, whereas plastic can only be recycled a certain amount of times before having to be downcycled.
In relation to some metals though, particularly the ones that are made with alloys, there may be chemicals like chlorine required to break them down. These chemicals may have the potential to be toxic or hazardous in some ways if not managed effectively.
Recycled metals like stainless steel still might still require new content in addition to their recycled content to make new products.
[Having said this, other metals like] aluminum, particularly aluminum cans, may truly be closed loop at can be recycled back into themselves (aluminum.org)
Plastic might be responsible for far more pollution (via littering and inadequately disposed of waste) at the end of material life cycle stage
Plastic usually takes far longer than metal to degrade in the environment
– Impact On Humans
Plastic may have the potential to impact humans in a number of ways – leaching of BPA and other chemicals, ingestion and inhalation of micro plastics, and so on.
Stainless steel and aluminum drink bottles may also have their own potential leaching issues when in use
– Impact On Wildlife & Environment
If either material finds it’s way into the environment, plastic may have more potential for negative impact on wildlife and the environment than metal via ingestion and entanglement in plastics
Micro plastics can also be a factor, as well as leaching of plastic additives into aquatic environments.
– Different Metals Compared To Each Other
[One study indicates aluminum has a] greater ‘cradle to gate’ (raw material) environmental impact in terms of energy required and global warming potential than stainless steel (greenlifestylemag.com.au)
Also from greenlifestylemag.com.au:
[When comparing aluminum to stainless steel via a life cycle assessment] aluminium was the worst performer for water use, stainless steel the worst for solid waste generation and the two metals the worst in terms of global warming impact.
Overall, stainless steel was a slightly better performer than aluminium due to lower emissions from the mining of its raw materials and the production process
Metal vs Plastic Furniture
Metal may win out over plastic furniture in health, and lifecycle, reuse and recyclability indicators (inhabitat.com).
Micro plastics in the air indoors that humans may inhale are also more closely linked to plastic furniture and textiles.
There’s also the consideration of which material can be made of recycled material: ‘… steel and aluminum furniture is likely already made of recycled content (inhabitat.com).’
Metal vs Plastic Bottles
Single use plastic bottles heavily contribute to waste and pollution problems. Metal bottles can be more sustainable than plastic bottles, but they usually need to be re-used over a longer period in order for their production footprint to average out to match plastic bottles.
Metal vs Plastic Packaging Items
Plastic packaging may be more sustainable across a range of environmental indicators compared to steel and aluminum … [and, using metal would result in a significant net negative environmental impact in the case of carrier bags, caps and closures, beverage containers, stretch and shrink film, other rigid packaging and other flexible packaging] (packaginginsights.com)
Read more about some of the potential issues with plastic packaging and plastic packaging waste in this guide.
Metal vs Plastic Construction Materials & Products
Both metal and plastic are used as building materials by themselves, and also in certain products (like windows and doors)
Both metal and aluminum can fit into the more sustainable and less sustainable categories for construction materials and products
For example, some metals may be more energy intensive than some plastics for certain applications
As another example, some plastic based window frames may have good thermal efficiency and insulation properties compared to some metal based windows, but may have challenges with recyclability
The Sustainability Of Plastic
Read more specifically about the sustainability of plastic in this guide.
This guide also outlines some of the overall pros and cons of plastic.
The Sustainability Of Other Metals vs Plastic
Aluminum vs Plastic Comparison
Stainless Steel vs Plastic Comparison
Other Factors To Consider When Comparing The Sustainability Of Different Materials
– Just as there are different types of plastic, there are different types of metal
Each different type of metal can have a different sustainability footprint, depending on how it’s extracted, refined, fabricated, and so on
– The waste management systems, facilities and technology in a given country or State make a difference to the sustainability not just of different materials, but different waste items and products
This is because of how different waste materials and items are processed among the different disposal options at different rates
– How long a metal product or item lasts, or how many times it can be used/re-used before being thrown out, impacts it’s sustainability footprint
– Whether the metal product uses recycled material or not impacts sustainability
– For metal products using recycled material, the amount of recycled vs new content used impacts sustainability
– Although there are general sustainability factors to consider with metal and plastic, the size, weight and other features of an item or product can impact sustainability too.
One material might be less eco friendly than the other per gram for example, but if the final product it’s used in is lighter than the same product made with another material, that product can have a better sustainability footprint even if the material itself isn’t as sustainable.