These types of lenses can be made from various different rigid plastic materials, formerly PMMA (Dk = 0) but now materials with higher gas permeability are commonly used. These lenses are highly customizable, allowing the practitioner to adjust and fine-tune a number of lens parameters to best fit the patient. Because of this, these lenses are well suited for patients with high corneal astigmatism or keratoconus. Because of higher silicone content, these lenses tend to be very hydrophobic, therefore in addition to a disinfecting solution these lenses would also require an application of a wetting agent prior to insertion to increase comfort of wear. These lenses are typically called “RGPs” or “hard contact lenses”.