Save the Children is calling on people to hold clothes swaps and scour vintage shops rather than buy new Christmas jumpers, after research found that 95% of the novelty items for sale contained plastic.

The appeal for consumer “sustainability” comes ahead of the charity’s annual Christmas jumper day on Friday, when it encourages supporters to buy and wear festive pullovers. Research by the environmental charity Hubbub estimates that 12m jumpers will be bought this year, triggering huge amounts of plastic waste.

Amid growing concerns over fast fashion and its effect on the environment, Save the Children said that rather than call off the fundraising day – which has raised more than £21m since its launch in 2012 – it was encouraging buyers to reuse and upcycle jumpers instead.

“As we have become more aware of the impact that fast fashion is having on the environment, we have been working hard to make sure that people can still take part in this annual event, without exacerbating the enormous climate problems we now face and which, we are aware, is one of the biggest threats to children around the world,” said Gemma Sherrington, the charity’s executive director of marketing and fundraising.

“Therefore we are trying harder than ever before for Christmas jumper day 2019 to be the most sustainable day yet. We are encouraging people to reuse old jumpers, buy jumpers from charity shops, hold jumper swaps and create their own – and if people really do need to buy a new jumper, we would encourage them to invest in one that they will wear for years to come.”

Hubbub’s analysis of 108 garments currently on sale from 11 high street and online retailers – including Primark and George at Asda – found that 95% were made wholly or partly of plastic materials. Acrylic was one of the most common plastic fibres found, occurring in 75% of the jumpers tested. Yet acrylic releases nearly 730,000 microfibres per wash, five times more than polyester-cotton blends, according to a recent study.

Many of the sweaters are expected to end up as single-use items, as two out of five Christmas jumpers are only worn once over the festive period, and one in three adults under 35 buys a new Christmas jumper every year.

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Save the Children said it was encouraging schools and offices participating in Christmas jumper day to hold jumper swaps and “bring and buy” sales. The charity has launched a recyclable bag that consumers can request online then use to donate old jumpers to sell in Save the Children charity shops across the UK.

Friends of the Earth encouraged consumers to reuse old jumpers and rethink their normal purchasing practices this holiday season.

“The Christmas novelty jumper has become a seasonal party staple, but resist the wear-once, throw it away variety – because it will just become landfill – and if possible look for one that isn’t made from plastic fabrics, like acrylic,” said climate and energy campaigner Tony Bosworth.

“If Rudolph pullovers are your thing, then don’t be afraid to wear it year in and year out – and resist feeling like you need Rudolph in a different colour each year to make a statement.”