During the washing process, all garments lose fibres. The fibres break from the structure of the fabric due to mechanical stress and abrasion. The broken fibres are typically 50 µm to 15 mm long and usually no thicker than 10 µm. 1µm = 0.001 mm or about 0.000039 inch. They could theoretically slip through the small openings of the GUPPYFRIEND Washing Bag. But they do not. To get through the opening, the fibre would have to poke vertically through the fabric. However, due to the water in and around the bag and the movement, the fibres are never positioned vertically, but always slightly bent. Therefore, they cannot pierce through the mesh. Even if a fibre should stick out of the fabric, it will be pushed back into the bag.