It's a good thing to be aware of, though, and it's a complicated problem. Rayon/viscose/bamboo (that is, processed cellulose textiles) do release a lot of microfibers. Early information seems to indicate that they biodegrade better than polyester/nylon/acrylic microfibers. Not perfect, but useful.

totally, would still prefer it over something entirely synthetic. the marketing just makes it feel a bit like "green washing". but maybe it's worth it in the long run if it moves folks back in the direction of more natural fibers