Most hair thickeners coat strands and thus are easily washed off, but newer versions add volume from within. In laboratory studies, L'Oréal Paris researchers have shown that the compound filloxane (also known as Intra-Cylane) penetrates the hair shaft, expands and strengthens the hair, and lasts for several washes. Similar to the silica gel used to fill cracks in car windshields, the technology is also inspired by wrinkle fillers for the skin, says Elisabeth Bouhadana, global scientific communications director for L'Oréal Paris. Added to serums or shampoos and conditioners, filloxane's small molecules slip through hair cuticles, attracted like magnets to proteins inside the fiber. They bind to the hair proteins as well as to each other, forming a rigid, stable network that adds volume to naturally thin or aging hair, according to the company's research. Hair reaches its maximum thickness after ten uses, and the effect lasts for five to ten washes after that, Bouhadana says. The ingredient (found in L'Oréal Paris Advanced Hairstyle Volume Filler products) is compatible with colored hair.