Fulldensity densifying spray treatment is a hair thickening spray with biotin that works on the surface of each strand to instantly expand the diameter by up to 9 for the sensation of up to 9 000 more strands after one usefulldensity densifying spray treatment is a hair thickening spray with biotin that works on the surface of each strand to instantly expand the diameter by up to 9 for the sensation of up to 9 000 more strands after one use