Polysiloxanes, also known as silicones, have an inorganic backbone of -(Si-O)- repeat units unlike most polymers. They are prepared through the hydrolysis of chlorosilanes or the ring-opening polymerization of cyclic siloxanes. Polysiloxanes have unique properties including flexibility from low rotation barriers, low surface tension, high stability, and high permeability to gases due to their large free volume. Their properties can be tailored by modifying the alkyl side groups along the backbone.