HI-BRUSH (Badger effect) and S-Brush (Hog bristle effect) synthetic fibers are made of PBT, a thermoplastic semi-crystalline polyester. Both filaments are corrugated as to improve the performance of the brush in terms of holding and releasing the lather during the shave. Both filaments are chemically tapered to give a soft touch on the skin. Synthetic fibers are really much more performing than hog bristle and badger hair. They better withstand their daily duty and are much more hygienic and easier to clean.