BosleyMD Professional Strength Hair Thickening Fibers – Medium Brown, 0.42 ozProduct Overview Experience instant fullness with BosleyMD Professional Strength Hair Thickening Fibers in Medium Brown. These keratin fibers bond to your existing hair to create the appearance of thicker, fuller strands that move naturally with you through the day. Why these fibers look and feel natural Hair is made of keratin and carries a positive charge. BosleyMD fibers are designed with a negative charge to create a subtle electrostatic cling.