This firm, flexible material makes up exoskeletons. Hacked primarily from dead insects.
— In-game Description

Chitin is a resource used in more advanced engrams. Chitin is harvested from certain creatures by punching them, using the Stone or Metal Pick, the Stone or Metal Hatchet, or carnivores. The most effective way being the Hatchet, Sabertooth, or Megatherium. Creatures with exoskeletons, namely invertebrates, will produce Chitin when harvested. 4 Chitin/Keratin is combined with 8 Stone in the Mortar and Pestle or 16 Keratin/Chitin can be combined with 32 Stone in the Chemistry Bench to produce Cementing Paste.