Cyanoacrylates are mainly used as adhesives. They require some care and knowledge for effective use: they do not bond some materials; their shelf life at room temperature is about 12 months unopened and one month once opened; they do not fill spaces, unlike epoxies, and a very thin layer bonds more effectively than a thicker one that does not cure properly; they bond many substances, including human skin and tissues. They have an exothermic reaction to natural fibres: cotton, wool, leather, see reaction with cotton below.