A further study by 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.
Based on its research, Hubbub has asked people to swap jumpers with friends by organising a "Christmas jumper amnesty" in places of work and schools.
Sarah Divall, a project co-ordinator at Hubbub, said: "We don't want to stop people dressing up and having a great time at Christmas, but there are so many ways to do this without buying new.
"Fast fashion is a major threat to the natural world and 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."