Hair Thickening Fibers are Keratin Proteins similar to natural hair. Hair Thickening Fibers blend with natural hair that may add density and help create thicker, fuller-looking hair. Provides instant results, can be used daily while your natural hair grows. Directions: Hair must be completely dry. Brush or comb hair, shake or use brush applicator of Bosley Pro, apply liberally into thinning and low-density areas and gently style hair into place.