*UPDATED* after 6 months of regular use (including 3 months of daily use) the zip broke off my GuppyFriend bag. Oh dear! But the customer service provided was excellent. I emailed the company on us@stopmicrowaste.com to raise my concerns and a replacement was dispatched swiftly.
If you invest (and I do mean invest as they cost upwards of £25) in a GuppyFriend bag to use in your washing machine, then you can trap the plastic-microfibres shed by the synthetic materials you wash.
In our GuppyFriend bag we wash; sports kit, fleece jumpers / jackets and fleece reusable baby wipes.
Please note that the GuppyFriend bag cannot be washed at over 40 C. For the outers of the 'Close Parent' Pop-In reusable nappies (which I wash at germ-killing 60 C, as they cannot be sanitiesd with Napisan - as Napisan degrades their waterproof layer) I use the ingenious Cora Ball from the Babi Pur website to trap the microfibre particles.
The GuppyFriend bag is big (60cm x 40cm) so it can fit an adult's fleece top in (with room to spare). The instructions say you shouldn't overfill the bag, or else the water will be trapped during the spin cycle leading to a soggier load of washing.
The bag feels like it is made of a silk-like fine mesh. It traps tiny plastic microfibres which would otherwise go into the waste-washing-machine-water, then into rivers, then oceans and from there into the food chain, meaning into the fish we eat - eek!
The GuppyFriend bag was designed by nature-loving surfers. Their Stop!MicroWaste website has comprehensive information about the problem of microplastics.