Lifecycle analysis: polyester vs cotton

Environmental consultant Clare Taylor of Clare Taylor Consulting on why understanding lifecycles allows you to identify where you can make a difference, using cotton and polyester as an example.

The lifecycle approach to environmental management is behind the circular economy, extended producer responsibility legislation and numerous high-level policies with good reason.

Lifecycle analysis, lifecycle assessment, lifecycle management and lifecycle approach are all closely linked, serving a common purpose – to understand and manage the impacts of a product or service throughout its life. Nothing affects the environment in just one way and looking at only a single issue or part of a lifecycle can lead to unwelcome, unintended consequences. A classic example was the push towards diesel cars because of their fuel efficiency: air quality and human health suffered as a result. 

Understanding lifecycles reduces such risks and allows you to identify areas where you can make the most difference. 

What are these tools and how are they useful to your business? 

The lifecycle of a product or service covers all the stages from acquiring the raw material through designing, making, and delivering your product or service, to its use and what happens to it at the end of its life.  

Carrying out a full lifecycle analysis (LCA) is a complex process, gathering large amounts of data to produce a detailed inventory of inputs and outputs. However, as better software and more LCA databases become available, this is becoming simpler and less time-consuming to do. 

Although waste is most visible at the end of the production process, it is usually created during steps taken at the beginning

It doesn’t necessarily include the lifecycles of everything used in the process: that is where scopes, system boundaries, functional units and allocations come in. Put simply, a functional unit allows comparison – so it could be an item, an amount of something or delivery of a specific service. Your scope and system boundary define what’s included, and you can use existing LCA information as available and needed to allocate impacts from outside the boundary proportionately.

Lifecycle assessment is evaluating the data. Both terms are often used interchangeably, though they are not identical. This assessment is useful when designing new products, materials or services as well as when planning policy and legislation.

Carrying out an LCA is not needed as part of a lifecycle approach – you can use existing information, including certain ecolabels or environmental declarations, but looking at the full lifecycle is still needed. In ISO 14001 it includes identifying what you can control and what you can influence as part of operational control. 

As an example, although waste is most visible at the end of the production process, it is usually created during steps taken at the beginning: in the design of the product, the specification, briefing the work in and planning production, and when ordering materials. The best gains are made by changes at the front-end. The impact of the waste is also easier to change here, by reviewing material specifications, perhaps, or designing and specifying for recyclability. 

An illustrative comparison 

An example of the way impacts and the ability to manage or influence them vary across a lifecycle can be shown by comparing a cotton shirt and a polyester shirt. This is a very simplified snapshot, ignoring the many other synthetic and plant-based fibres available, which all differ in their impacts, and leaving out a lot of detail (which would need a book) but will give the general idea.

A common belief is that cotton is the better environmental choice because of microplastic pollution, a serious concern as manufacturing and laundering synthetic clothing account for about a third of microplastics in the environment – but is it as straightforward as that? Here are some of the questions that arise. 

Impact on natural resources

Acquiring the textile to make our shirt requires cotton to be grown. Cotton is a natural, renewable fibre, but has the highest negative impact on ecosystems per kilogramme than any other fibre used for garments. This is down to the very high use of fertilisers and pesticides, and their effect on biodiversity and contamination of soil and water as they seep through the soil or are washed off by rain and reach water sources. Growing cotton uses significant volumes of water (and land), damaging ecosystems, whereas polyester’s water footprint is lower. 

Polyester is a fossil-based plastic with no agriculture involved; manufacturing has lower impacts on ecosystems than growing cotton, but there are the impacts of acquiring the oil.

Over its lifecycle, polyester's greenhouse gas emissions are generally less than those of cotton

Impacts at this stage can be affected by many things, such as initiatives for more sustainable cotton farming, organically grown cotton and use of recycled polyester. Bio-based sources of polyester are being developed, but there is the risk of them competing with food production or having other ecosystem impacts.

Garment production and use

When making the garment, the considerations are similar for both: what chemicals are used, what controls there are in place to prevent pollution to water and air, including microfibres as textiles are cut and made up. Microfibres are not unique to polyester – they arise from all textiles, and natural microfibres are also damaging to human health and the environment.

Textile fibres in the air particularly affect workers in the industry. There are still differences between the two textiles – dyeing polyester is a less intensive process than dyeing cotton, for example.

Again, there are initiatives in place to reduce manufacturing impacts, particularly in fabric dyeing.

In its use phase, the impacts of either are dependent on the user. As polyester is lighter, you can potentially have more items in the washing machine, using less water and detergent per item, but it releases significant volumes of microplastics to the water. Cotton also releases microfibres at this stage, and research to quantify this and determine its impacts is ongoing. Although treatment at sewage plants can capture a high proportion of microfibres, the practice of using treated sludge on agricultural land can return them to the environment. 

How much microfibre is released during use depends on consumer choice – wash cycle, how full the machine is – but also on whether the clothes are washed within a filter bag or filtered by the machine. Very few currently have suitable filters, but there are retrofit filters now available, and the first machine with a built-in microfibre filter was launched in 2021. Microfibres are released into the air during tumbledrying.

Energy and climate change

Polyester has a higher energy impact at the stage of acquiring the textile as its manufacture is an energy-intensive process. In use, however, the picture is very different and over its lifecycle its greenhouse gas emissions are generally less than those of cotton.

Polyester is an easy-care fabric – it dries more quickly than cotton and needs less ironing. The energy consumption of tumbledrying is greater than that of washing, so the shorter drying time of polyester is significant. 

There are no easy answers, but there are a lot of intervention points where impacts can be reduced

Energy in the use phase is very high for both textiles and, again, controlled by the consumer, but can be influenced by clothing labels and campaigns to wash at lower temperatures.

Behaviour here not only relates to washing temperature but also washing frequency, the type and duration of the wash cycle and how clothes are dried (whether line-dried or tumbledried), how often they are ironed and at what temperature. 

End of life

Polyester can be chemically recycled without loss of quality. Cotton can be recycled mechanically, but its fibres become shortened and it needs the addition of virgin fibre, which can be synthetic or another cellulose fibre. It can also be chemically recycled into a different cellulosic fibre, but this is new technology and not readily available at commercial scale. Clothing made of a single fibre type is easier to process.

Again, consumer choices play a large part, with most clothing being disposed of rather than being recycled, and little being repaired to extend its life.

An effective area of influence here is the durability of the item of clothing. Good-quality textiles and well-made garments can be worn for longer, so the impact up until the use phase and at end of life is spread out over a greater number of ‘wearing days’ and, in addition, defers the need for replacement.

Is there an easy answer?

As you can see, it is a very complicated question. Factor in too the different use cycles of non-clothing textiles and, to look beyond just environmental impacts into sustainability, the social impacts of the textile industry and it becomes even more so. There are no easy answers, but there are a lot of intervention points where impacts can be reduced.

Ecolabels and environmental declarations help with choices, but they need to be robust and evidence-based to serve their purpose.

None of this is static. There are programmes and initiatives to reduce impacts of all types of textiles and clothing at all stages in the cycle. Work is also ongoing to understand and reduce the release of microfibres from textiles – an EU project and cross-industry initiatives aim to tackle filtering microfibres out from water and work to prevent their release to the environment.

And, of course, we can all make an individual difference in our own choices in our personal lives.