<prompt> The material of soft lens ?PolymethylmethacrylateHydroxymethylmethacrylateSiliconCellulose acetate Butyrate  <response>: Types of contact lenses- Depending upon the nature of the material used in their manufacturing, the contact lenses can be divided into three types:- Hard lenses: Made of polymethylmethacrylate PMMA Rigid gas permeable PGR lenses:- Copolymer of PMMA, silicon-containing vinyl monomer and cellulose acetate butyrate CAB are used to manufacture RGP lenses Soft lenses:- These are made up of hydroxymethyl methacrylate HEMA. Reference : AK Khurana Comprehensive Ophthalmology, 6th edition, pg no. 208 - 209 