Isdin Si Nails: improves nail hardness and flexibility. It is a fast-absorbing nail strengthener with an invisible finish that, thanks to its combination of ingredients, promotes healthy and strong nails. Key Components Hyaluronic Acid Organic Silicon Pistacia Lentiscus Indication Improves nails hardness How to use Si-Nails nail strengthener is a clear, lightweight serum delivered by an easy-to-use, one click applicator pen, applied once a day. It can be applied to nails with colored nail polish. The first time you use Si-Nails, activate the brush by pressing down on the applicator until the brush is moistened (approximately 25 times). After first use, just click once for each nail you would like to apply it to. Visible results may be seen in 14 days, with best results achieved from ongoing application.