a complex chemical substance (C8H13O5N) that forms the hard shells of insect bodies (it is the basic substance of insect cuticle), the skeletons of some fungi and parts of the bodies of bryophytes, but also the cell walls of some plant fungi (Fungi)

Chitin is very durable and flexible, it does not decompose easily. In the cuticle, it is often strengthened by the protein sclerotin or by mineral salts, especially calcium salts. We call such a strengthened cuticle sclerotized (not chitinized, because every cuticle is like that).