The earliest models of soft contact lenses, based on hydrogel material, had a level of oxygen permeability of around 6–8 Dk/t.
[1] Polymacon, the material used in the first hydrogel contact lenses in some countries in the 1960s and approved by the FDA in the U.S. in 1971, has a Dk of 9 .
These days, typical values of oxygen permeability for hydrogel contact lenses range from 25 to 50.
D being diffusivity (cm2/sec) – a measure of how fast the oxygen moves through the material.
Note, different sources may use different units: contact package inserts often use cm2/sec, while academic papers may use other values for distance such as mm2/sec.