Will flannel fabric pill? Are flannel coats made of flannel fabric good? Flannel fabric is prone to pilling, and there are three main reasons for this. Firstly, the quality of the flannel coat largely determines whether it will pill or not. Most flannel coats are made of a blend of pure wool and other fabrics, which may cause some pilling, but the extent of pilling is usually limited. Secondly, the composition of the fabric itself, whether pure or blended, will affect the quality of the coat. Finally, if the wool is too short or the knitting density of the flannel is too high, it will easily cause pilling. When purchasing flannel coats, it is important to choose those with quality and reputation guarantees.