What materials release microplastics when washed?

Hi I buy pretty much all my clothes second hand so I don’t need to worry too much about environmental harm during production. However, I do try to buy natural and biodegradable clothes anyway (e.g. cotton, wool) to reduce microplastic pollution from washing and general quality/comfort/performance. However, there is the odd thing that it’s very difficult or even impossible to get 100% natural fibres - such as a suit or some sports/outdoors wear. I know you can get suits with natural lining such as cotton but they’re quite hard to find and even more so second hand! Does anyone have any info on synthetic or semi-synthetic materials that have a minimal environmental impact (barring its production given I’m looking second hand). Thanks for any help. Details on biodegradability of the material would also be interesting but obvs not the main thing as I’m buying clothes already in the second hand market.