Compositions including polycarbodiimide and derivatives thereof together with f amino silicone compounds and derivatives thereof to enhance the quality of the keratinous substrates. The present invention relates to a cosmetic treatment and process for treating keratinous materials, in particular for hair-care and hair-styling, wherein the composition can include the polycarbodiimide and the amino silicone compound in amounts sufficient to impart hydrophobicity to keratinous substrates, including hair fibers, upon application thereto. It is in particular a hair treatment composition and process for enhancing durable non-permanent shaping and curling of the hair.