This is a Rosco Permacolor Glass UV Pass Woods-type Filter. The Permacolor Standard Colors dichroic filters are durable glass color filters that transmit only certain wavelengths of light, reflecting the rest of the spectrum, rather than absorbing it.
Since virtually no energy is absorbed by the filter, light transmission is significantly higher than traditional gels and will never burn out or fade.
The Permacolor filters are made with the highest quality coatings, designed not to fade or shift color.
In addition, Rosco's sophisticated manufacturing process allows for precise color consistency batch to batch to a degree that is unprecedented in other dichroic coatings.