Fibre Thickening Serum Formulated with powerful ingredient Intra-Cyclane It increases the thickness of your hair. The intelligent Serioxyl Thicker serum by L'Oréal Professionnel instantly re-densifies hair and leaves it feeling fuller and thicker thanks to its unique formula combination of thickness-bootsing activities by L'Oréal Advanced Research. Instant thickening effect for thin or fine hair. Enriched with Intra-Cylane™. L’Oréal Professionnel Serioxyl Thicker Hair Serum can give you thicker looking hair in an instant. Enriched with the formula Intra-Cylane, it can give thinning hair an instant thickening effect, allowing you to create your desired look.