The Guppyfriend Washing Bags are made of polyamide 6.6. This is a high-tech material and is particularly tough and resistant to alkalis. The fabric itself doesn't shed any microplastic fibres because it is made of monofilaments. These are more like stable sticks than threads, which are made from several fibres and are typically used for textiles. The binding tape consists of long staple fibres. Even if these should become detached from the bond, it is unlikely that they will break off.