The Designer’s Compass - Part 2: Threadbare Truths and High-Heat Emissions: Balancing Reuse in Textiles and Metals

Metals and textiles are fundamental categories in product design. Both material families boast exceptional durability and established recycling potential. However, each presents distinct, complex sustainability challenges for designers.

Textiles face a profound recycling problem caused by material complexity and low recycling rates. Conversely, metals face a serious emissions problem due to their high energy demands during production. Designers must understand both these challenges to make truly sustainable material choices.

The Complex Web of Textiles

Textiles are a complex family of materials crucial for products ranging from furniture to automotive interiors. They divide broadly into woven fabrics and non-woven materials, such as leather and synthetic films. Assessing the environmental impact of textiles is difficult.

The material life cycle involves extensive processing steps beyond the raw material origin. This includes spinning fibers into yarn and weaving or knitting the final fabric. Each step relies on a vast array of chemicals. These chemicals include fertilizers and pesticides for natural fibers like cotton, as well as spinning oils and sizing chemicals for pre-treatment. Finishing processes, such as dyeing and printing, add further layers of complexity, impacting toxicity, water footprint, and durability.

The Recycling Disconnect

Textile recycling rates remain low globally. Designers must understand that most commercially available recycled textile fibers do not originate from discarded textiles. Recycled polyester (PET) textiles, for example, rely almost entirely on waste PET bottles from the plastic industry. Similarly, recycled polyamide (PA) textiles frequently use waste materials from other industries, such as recovered fishing nets or carpets.

This disconnect exists because the processes available today make it difficult to efficiently re-spin mechanically shredded textile waste into new yarn. Consequently, actual textile recycling mainly includes cotton and wool. Recycled textiles accounted for only about 0.4% of the total 6.5 million tonnes of cellulose-based synthetic textiles produced globally in 2020.

The Mixed Fiber Problem

Recycling is complicated significantly when textiles consist of blends of different fibers. Common examples include cotton mixed with elastane for stretch or cotton mixed with polyester (PET) to reduce pilling. Currently, very few specialist recyclers possess the capability to process and separate these mixed-fiber textiles.

Designers must avoid these mixed-fiber materials. Achieving desired properties, such as stretch or anti-static performance, should ideally happen with a single, mono-material textile. This commitment to single materials improves the likelihood of successful recycling at the product’s end of life.

Innovations in Textile Circularity

Mechanical recycling, which involves grinding and shredding, is problematic for mixed textiles. Chemical recycling offers a promising avenue for textile circularity. Chemical processes can break down plastic waste into its core chemical building blocks.

Chemical recycling offers advantages over mechanical recycling. It can often recycle mixed textile waste. Furthermore, it removes contaminants and additives, such as dyes and inks. This purification allows the resulting recycled fiber to be finished in the same way as virgin material. Examples include Ambercycle™ Cycora® chemically recycled PET textiles and Lenzing REFIBRA™ Lyocell, partially made with chemically recycled cotton. However, designers must note that chemical recycling processes are often considerably more energy-intensive than mechanical recycling, at least currently.

Renewable Textiles

Renewable textiles, derived from plants and animals, accounted for an estimated 37 per cent of total global textile production in 2020. The environmental impact varies significantly within this category.

Hemp and jute grow on non-agricultural land with minimal irrigation. Conversely, cotton requires good soil and substantial water supplies. Conventional cotton cultivation often uses large amounts of petrochemical-based fertilizers and pesticides. Initiatives like organic cotton and Better Cotton aim to reduce the environmental footprint by limiting or eliminating these chemicals.

Textile Material Profiles and Metrics

Textile environmental impact assessments usually include Global Warming Potential (GWP) measured in kilograms of CO2 equivalents per kilogram of material. Recycled materials consistently offer substantial GWP reductions compared to their virgin petrochemical-based counterparts.

Recycled Polyester (PET) Textiles: Recycled PET textiles boast good strength, durability, and water resistance. The clarity of PET bottles makes it straightforward to color the recycled textile, similar to virgin material.

Recycled Polyamide (PA) Textiles: Virgin PA has a large environmental footprint, making recycled options very attractive. Recycled PA woven textiles show excellent durability and toughness. Virgin PA6 textile production uses 148 MJ/kg of energy, contrasting sharply with the energy efficiency of the Aquafil ECONYL® PA6 textile.

Recycled Cotton Textiles: Recycled cotton primarily comes from post-industrial waste. Recover™ RPure recycled cotton has a GWP of only 0.2 kg CO2e / kg fiber, significantly lower than virgin cotton’s 1.8 kg CO2e / kg fiber. Virgin cotton production demands massive resources, requiring up to 2,100 liters of water per kilogram of fiber. Pure cotton textiles are also compostable, offering a robust end-of-life option.

Recycled Wool Textiles: Wool recycling has a long history. Recycled wool from Manteco® MWool® has a GWP of 0.6 kg CO2e / kg fiber, a dramatic reduction from virgin wool’s median GWP of 75.8 kg CO2e / kg fiber. Recycled wool textiles are highly durable and offer good breathability and abrasion resistance.

Recycled Leather (Bonded Leather): Recycled leather, often called bonded leather, uses post-industrial leather waste that is ground up and mixed with a resin binder. Virgin leather production has a massive environmental footprint, including a GWP of 41.5 kg CO2e / kg and water use of 32,800 liters per kilogram. Recycled leather dramatically reduces this footprint, with an estimated GWP of 16.6 kg CO2e / kg.

The Energy Crisis of Metals

Metals possess exceptional strength and longevity, but their production is enormously energy-intensive. The industry represents a major source of global CO2 emissions.

In 2021, just 553 global steel plants accounted for 9 per cent of total global CO2 emissions. Aluminum production is even more energy-intensive, generating up to 20 kilos of CO2 for a single kilo of material. Mining for raw materials is also destructive, causing permanent land scars. Unmanaged mines risk contaminated wastewater leaching into local soil and waterways. Designers should seek out suppliers who comply with certifications like the Initiative for Responsible Mining Assurance (IRMA), which promotes responsible mining standards.

Benchmarking Metal Emissions

Comparing the environmental impact of different metals requires caution. Global Warming Potential (GWP) is commonly measured in kilo of CO2 equivalents per kilo of material. However, this metric can be misleading for metals because material density varies widely. Steel has about three times the density of aluminum.

Therefore, comparing emissions based on the weight of a specific part, rather than simple kilo-for-kilo comparison, offers a more accurate result. For example, the emissions of primary aluminum are roughly a third of primary steel when compared by weight, but this comparison shifts significantly when adjusted for volume.

Metals are durable and highly valuable, making them one of the most widely recycled material categories globally. This high recyclability means metals are infinitely recyclable in theory, with little to no loss of quality. The International Aluminium Institute estimates that approximately 75 per cent of the 1.5 billion tonnes of aluminum ever produced is still in use. Global production uses, on average, 35 per cent recycled steel and 32 per cent recycled aluminum.

Recycling Processes and Purityble, making them one of the most widely recycled material categories globally. This high recyclability means metals are infinitely recyclable in theory, with little to no loss of quality. The International Aluminium Institute estimates that approximately 75 per cent of the 1.5 billion tonnes of aluminum ever produced is still in use. Global production uses, on average, 35 per cent recycled steel and 32 per cent recycled aluminum.

Recycling Processes and Purity

Metals are relatively easy to separate from other waste streams. Magnetic metals like steel are pulled out using powerful magnets. Non-magnetic metals like aluminum use an eddy current separator, which employs electric currents for separation. High-temperature re-melting during the recycling process effectively burns off surface coatings, adhesives, and other contaminants.

The complexity arises in sorting different grades and alloys. Aluminum recycling is particularly complex. Aluminum alloys are formulated for specific properties and processes. To preserve material properties, these alloys must be sorted and recycled separately. For example, 6000-series aluminum, often used for extrusion, must be separated to retain its suitability for anodizing.

Foundry alloys (4000-series) are suitable for casting but contain silicon, which makes them unsuitable for anodizing. These alloys allow greater flexibility during the recycling process, permitting the mixing of different alloys.

Designing for Metal Circularity

Designers should always distinguish between post-industrial recycled (PIR) factory waste and post-consumer recycled (PCR) waste. Recycling PIR scrap should occur, but excess PIR suggests inefficient processing upstream. Suppliers should confirm the ratio and origin of recycled content.

Crucially, product assemblies that combine metal with other materials must be designed for easy separation. Designers should use integrated features like click joints and slots, or mechanical fasteners like screws, rather than adhesives or thermal bonding. For example, Richard Hutten designed the Blink seating for Schiphol Airport using only screws for assembly. This choice ensures the aluminum can be easily disassembled for replacement or recycling, promoting longevity and circularity.

Recycled Metal Profiles and Metrics

Recycled metals require significantly less energy than virgin production. Hydro CIRCAL 6000-series aluminum, which uses 75% PCR content, has a GWP of <2.3 kg CO2e / kg, dramatically lower than the 11.3 kg CO2e / kg GWP of virgin 6000-series aluminum.

Recycled stainless steel from Outokumpu, which uses at least 90% PIR and PCR waste, achieves a GWP of 3.4 kg CO2e / kg, significantly reducing the virgin GWP of 7.7 kg CO2e / kg. Recycled steel, such as ThyssenKrupp Bluemint® Recycled, which uses 100% PIR and PCR waste, achieves a GWP of >0.75 kg CO2e / kg, compared to 2.4 kg CO2e / kg for virgin steel.

The Push for Low-Carbon Metals

The high environmental footprint of virgin metal production necessitates a shift toward low-carbon processes. Metal suppliers are actively seeking alternative energy sources and efficiency improvements.

Aluminum smelters historically built near renewable energy sources, like hydro- and geothermal power plants, minimize emissions. However, more than half of global aluminum production still relies on coal and natural gas power. The Norwegian supplier Hydro developed Hydro REDUXA low-carbon aluminum, which utilizes renewable energy and improved efficiency, achieving a GWP of 4 kg CO2e / kg. This figure is among the lowest emissions for primary aluminum globally.

For steel, traditional processes rely on burning coke, a major source of CO2 emissions. Long-term solutions involve hydrogen. The Swedish supplier SSAB developed HYBRIT low-carbon steel, which replaces fossil fuels with renewable energy and “green” hydrogen. ThyssenKrupp Bluemint® Pure low-carbon steel achieves an extremely low GWP of 0.6 kg CO2e / kg.

Low-carbon steel production also explores replacing traditional iron ore with Direct Reduced Iron (DRI) or Hot Briquetted Iron (HBI), which require less energy. The use of hydrogen in this process eliminates fossil fuels altogether.

The shift toward low-carbon metals demands designers specify materials not just based on recycled content, but also on the energy sources used in virgin production. For example, the Emmaljunga NXT90 ERGO stroller uses Hydro REDUXA low-carbon aluminum profiles, focusing on the material’s clean energy origins.

Summary

Designers navigate a challenging material landscape where sustainability is never a simple choice. Textiles struggle with achieving high-quality recycling due to complex material blends and low collection rates. Metals excel at recycling but must overcome the huge energy demands of primary production. By prioritizing mono-material textile design, promoting chemical recycling innovations, and demanding low-carbon metal sourcing, designers can successfully guide products toward a circular economy.

Making a sustainable material choice is like choosing a boat for a long voyage [i]. For metals, you must pick a vessel that uses clean winds (low-carbon energy) from the start, as building the hull is the hardest part. For textiles, you must ensure the fibers are not knotted together (mixed materials) so that they can be easily rewoven into a new sail when the old one wears out.