The Hoya HRT Circular Polarizer-UV filter uses a high-rate transparency polarizing film that passes more visible light through the filter while still filtering the same amount of polarized light. The filter blocks only 1.1 stops of light which is around 2/3 to 1 full-stop better than a standard circular polarizer.
The glass of the HOYA HRT filter also has ultra-violet (UV) absorbing properties making the HRT a combination UV/circular polarizing filter. The most common use for a circular polarizer filter is to darken blue skies in outdoor photography, but they can also reduce or eliminate reflections from non-metallic surfaces such as glass and water. By rotating the outer ring of the filter, the change of effect can be seen by looking through the filter or through the viewfinder if it is mounted on a camera.