Every textile loses microfibers, but it is the synthetic materials (polyester, acrylic, nylon, etc.) that shed the harmful fibers. Most apparel contains synthetic fibers to some degree (unfortunately, sometimes it is not stated on the label).
You can also put pure cotton and wool inside the bag. Textiles from natural materials also lose fibers. The bag reduces fiber breakage and thus protects your garments and reduces wear and tear. You’ll enjoy your clothes much longer – another sustainability benefit of the Guppfriend Washing Bag.