Gas permeable contact lenses are considered hard lenses, but should not be confused with the hard contact lenses of the past.  In the past, hard lenses were manufactured using the material polymethyl methacrylate, known as PMMA.  Previous to 1971, when the soft contact lens was introduced, almost all contact lenses were made using this material.  PMMA lenses were not easy to get used to and could be quite uncomfortable, and PMMA lenses do not allow oxygen to the eye, which is extremely unhealthy.

Introduced in 1979, the technology for gas permeable lenses is actually more recent than that of soft lenses.  Gas permeable lenses, also known as RGPs, rigid gas permeable, or oxygen permeable lenses, are made using silicone, a more flexible material than PMMA.  Silicone allows oxygen to enter the eye, more so than soft contact lenses, actually.

Gas permeable lenses give patients superior visual acuity, are durable and better deposit resistance than soft contact lenses.  These lenses can be easier to clean and are generally less expensive in the long run because of their long life span.

Since gas permeable lenses are made of rigid material the lenses keep their shape when you blink, giving you crisp vision.  The rigid material makes them durable and hard to rip and because they are made of with materials that do not contain water, protein and lipids from your tears have difficulty binding themselves to the lenses.  As long as you do not require a prescription change, gas permeable contact lenses can last for years.