CO₂ footprint of engineering plastics

The question of the CO₂ balance of materials has long since become a decisive factor in industry. Companies no longer focus solely on price, stability and functionality, but also on the environmental impact of the materials used. A particular focus: the comparison of engineering plastics with classic metals such as steel or aluminium.

More and more decision-makers from industry are therefore examining not only technical specifications but also the ecological consequences of their material choice. At the same time, customers, investors and policymakers increasingly demand transparent information on the ecological footprint. Those who act with foresight here can not only reduce costs but also strengthen their own market position and improve their company image.

Why the CO₂ balance is becoming increasingly important

Industry is under growing pressure to reduce its emissions. Political requirements such as the European Green Deal, stricter emission limits and sustainability reports based on ESG criteria mean that the CO₂ balance has become a strategic management tool. Customers and end consumers, too, are increasingly choosing more sustainable products. At the same time, CO₂ certificates and rising energy prices are driving up the costs of energy-intensive materials.

Materials therefore play a key role, since production, transport, use and recycling feed directly into the life cycle assessment. In many applications, engineering plastics are now used as an alternative to metals – not only for functional reasons but also for ecological ones. Particularly where weight reduction, energy efficiency or design freedom are required, they are increasingly regarded as a forward-looking solution. A forward-looking choice of material can thus create not only ecological but also economic advantages and, in the long term, determine a company's competitiveness.

Production: energy demand and emissions compared

• The production of metals is traditionally extremely energy-intensive.
• Due to the melting and electrolysis process, aluminium has an extremely high primary energy demand.
• Steel causes high CO₂ emissions in classic coal-fired blast furnaces; electric steel reduces these in part.
• Engineering plastics require energy for polymerisation, extrusion or injection moulding, but are usually below the emission values of metals.

Material	CO₂ emissions from production (kg CO₂/kg material, approximate)	Special features
Aluminium	8–12	Very high energy input, heavily dependent on the electricity mix
Steel	1.7–2.5	Emission-intensive in the blast furnace process, electric steel with better values
POM, PA, PEEK (engineering plastics)	2–6	Dependent on the raw material base (fossil/bio-based) and additives

• Plastics can be used in smaller cross-sections thanks to precise shaping.
• Metals often require more massive designs, which increases the material requirement.

A further aspect: plastics can be used in smaller cross-sections thanks to precise shaping, while metals are often required in a more massive design. This further reduces the material requirement.

Use: weight advantages and energy efficiency

Probably the greatest advantage of plastics over metals lies in their weight. A component made of plastic can be up to 70% lighter than its metal counterpart. In industries such as the automotive industry, this weight saving leads to lower fuel consumption and lower emissions over the entire life cycle of the vehicle. In aviation too, this effect is enormous: every kilogram saved reduces the CO₂ burden considerably in the long term and lowers operating costs. Similar advantages are seen in medical technology or in mechanical and plant engineering, where the use of lightweight components saves energy during operation.

The lower weight of plastic components also affects secondary factors: motors, drives or conveyor systems have to move less load, which further increases energy efficiency. In many cases, designs can be made more compact, since the lower material density of plastics allows greater design freedom. In addition, thanks to their vibration-damping properties, plastics improve comfort and reduce wear on adjacent components.

Metals, in turn, impress with their high resistance to temperature, pressure and abrasion. In certain applications, they thereby considerably extend the service life of components – which can partly offset the ecological disadvantages of production. If a metal component is used over decades, this can result in a very good CO₂ balance. The specific application is therefore decisive: if a plastic part is replaced more frequently due to lower resistance, the positive balance can be relativised again. Conversely, where plastics are used in a durable and efficient way, they can play to their strengths to the full.

Transport and logistics

Transport should not be underestimated either. The lower weight of engineering plastics reduces energy consumption throughout the entire logistics chain. This affects not only road transport but also shipping, air freight and internal material flows. A container full of plastic parts can weigh considerably less than a container full of metal parts for the same number of units. The result: lower fuel consumption and lower CO₂ emissions across the entire transport chain. With metals, this advantage is smaller, since the high density places a heavy burden on transport volume. For globally operating companies, the difference between plastic and metal components can mean considerable emission savings over the years.

Recycling and the circular economy

Recycling plays a central role in the CO₂ balance. Metals are unbeatable here: aluminium can be recycled almost indefinitely, and with an energy demand of only about 5% of primary production. Steel also achieves recycling rates of over 90% and fully retains its properties.

Plastics, by contrast, face major challenges. Although established recycling processes exist for commodity plastics such as PE or PET, engineering plastics often have a more complex structure: glass-fibre-reinforced, provided with additives or processed into composite structures. This makes single-grade recovery more difficult.

However, newer processes such as chemical recycling or depolymerisation open up prospects for recovering high-quality raw materials from waste materials. There is also growing interest in closed material cycles in which companies organise the take-back and recycling of their own plastic products themselves.

Future prospects: CO₂-optimised materials

Materials research is working intensively on solutions to further improve the CO₂ balance. In the metals sector, the focus is on low-CO₂ production processes, such as hydrogen-based steel production or aluminium from renewable energy. In plastics, bio-based polymers, CO₂-neutral additives and the increased use of recyclates are key topics.

Hybrid material solutions too – for example plastic-metal composites – are being increasingly developed in order to combine the advantages of both materials: the lightness and freedom of form of plastics with the strength and recyclability of metals. In addition, digital technologies such as AI-supported material simulations are gaining importance in order to optimise the CO₂ balance of new materials already during the development phase. In future, companies could achieve not only an improved life cycle assessment but also regulatory and competitive advantages through intelligent material selection.

Holistic view: life cycle and application

A blanket statement about which material is more sustainable falls short. Only a complete life cycle assessment (LCA) provides a realistic picture. Here, raw material extraction, production, transport, use and disposal are considered together. In some cases, a lightweight plastic may be the better choice despite poor recyclability, while in durable high-performance applications metal remains superior.

The end-of-life scenario is also decisive: can the material be recycled or thermally recovered, or does it end up in landfill? Social and economic aspects are also increasingly included in the sustainability assessment. Companies are therefore well advised to make material decisions not in isolation but in the context of the entire value chain and life cycle.

Summary

The comparison shows: engineering plastics can offer considerable advantages over metals with regard to the CO₂ balance, above all through the lower energy demand in production and through the lower weight in use. Metals, by contrast, score with almost perfect recyclability and high durability. Which solution is more sustainable depends heavily on the application.

In the long term, the CO₂ balance of both material groups will be further improved – through renewable energies, new recycling technologies and innovative material developments. For companies, this means: the choice of material should not be made in isolation but always within the framework of a holistic life cycle assessment.

FAQ

Why are plastics often more climate-friendly than metals? Because their production usually requires less energy and, thanks to their low weight, they can save CO₂ during use.

Do metals not always have the better life cycle assessment because of recycling? In recycling, yes, but in the primary process metals are often significantly more energy-intensive than plastics.

What role do bio-based plastics play? They can improve the CO₂ balance by replacing fossil raw materials. However, their sustainability depends on cultivation, land use and recyclability.

How is the CO₂ balance of metals developing? With low-CO₂ steel from hydrogen reduction or aluminium from renewable energies, emissions will fall significantly in future.

Which factors should companies consider when choosing materials? In addition to pure production emissions, service life, weight savings, transport routes and recyclability also count. Only in this way can a well-founded decision be made.