Most Christmas jumpers expected to be sold in the UK this year are made with plastic, a study has found.
Environmental charity Hubbub has warned against buying the seasonal garments after finding that up to 95% of them are made using plastic.
Consumers are urged to buy them second-hand or to swap old ones with friends.
The charity estimates UK shoppers will buy 12 million festive jumpers this year, despite already owning 65 million from previous years.
A spokeswoman for Hubbub described the Christmas jumper as “one of the worst examples of fast fashion” and warned that such consumer habits are a “major threat” to the planet.
In a survey, the charity found that two-fifths of the festive tops are worn just once during the Christmas period.
The survey of more than 3,000 UK adults also suggested that one in three people under 35 buy a new sweater every year, while only 29% of shoppers know that most Christmas jumpers contain plastic.
Hubbub analysed 108 jumpers available to buy this year from 11 High Street and online retailers, and found that 95% were made wholly or partly of plastic materials.
Three-quarters of the garments tested contained acrylic, making it the most commonly used plastic fibre. Some 44% were made entirely from acrylic.
In 2016, a study by Plymouth University found that acrylic was responsible for releasing nearly 730,000 microfibres per wash – five times more than polyester-cotton blend fabric, and nearly 1.5 times as many as pure polyester.
In a statement, Hubbub project co-ordinator Sarah Divall said fast fashion is a “major threat” to the natural world, adding that “Christmas jumpers are particularly problematic as so many contain plastic”.
“We’d urge people to swap, buy second-hand or re-wear – and remember a jumper is for life, not just for Christmas,” she said.
The warning comes ahead of Save the Children’s annual Christmas Jumper Day, which returns on Friday 13 December.
The event sees tens of thousands of schools and workplaces across the UK take part by encouraging people to wear a festive jersey.
The charity urges participants to wear their “daftest woollies” and donate £2 each.