Around half of clothing sold by the biggest online “fast fashion” retailers is made from new plastics such as polyester, according to a new report from the RSA.

Researchers for the Royal Society for Arts, Manufactures and Commerce (RSA) analysed 10,000 garments added to the Asos, Boohoo, PrettyLittleThing and Missguided websites over two weeks in May and found that an average of 49% were made entirely of new plastics such as polyester, acrylic and nylon.

The study found that as much as 88% of the recently listed items on PrettyLittleThing contained new, or virgin, plastics. For some stores, only 1% of garments contained recycled materials. “Some online stores have been slow to adopt recycled materials in their clothing,” the report added.

The RSA published the report, Fast Fashion’s Plastic Problem, today to highlight the poor record of sustainability in “fast fashion” in the UK, written by Will Grimond and Josie Warden.

It concluded: “Some companies have a mountain to climb if they are to meet their own sustainability targets. These companies are ‘greenwashing’ their images by producing small sustainable ranges, while the bulk of their output is still made from petrochemicals.

“Fast fashion shoppers may not be aware of the amount of plastics they are buying. Previous RSA research suggests just half of those who shop at fast fashion websites say they regularly buy clothes containing synthetic materials, despite plastics being highly prevalent in online stores.”

The RSA report highlighted the environmental cost of plastics in fast fashion. “Synthetic textiles are creating significant environmental damage in terms of emissions and waste. An MIT study found that the average polyester shirt produces 5.5kg of CO2, 20% more than its cotton equivalent, and the same emissions as driving 13 miles in a passenger car.”

In 2015, polyester production was responsible for 700 million tonnes of CO2 – the equivalent of the annual carbon emissions of Germany.

Deficiencies in the UK’s recycling system means that a lot of this plastic is likely to end up in landfill. Petroleum-derived fabrics make up a large amount of the trillions of microfibres that are showing up in the world’s rivers, oceans and food systems.

Retailers have committed to improving their record on the use of plastics. Missguided has pledged to ensure that 10% of its products use recycled fibres by the end of 2021 and 25% by the end of 2022. Asos is increasing the use of recycled synthetics and sustainable cotton in garments it sells and has introduced a “responsible edit” to help shoppers understand which garments are made with more sustainable fabrics.

Click here for the full free downloadable report.