A quote from their website;
Most other filter manufacturers start with ordinary window glass that has been poured in thin sheets and cooled quickly, introducing internal flaws. B+W filters, on the other hand, start with a cylinder of Schott German optical glass from which the filters are diamond cut, precision ground, and then polished to ensure flatness on both surfaces and uniform thickness throughout. Every B+W filter is interferometrically tested for plane parallelism. This process is used routinely by the world’s leading lens makers, but only rarely by filter manufacturers.
To reduce unwanted reflection and lens flare, which can seriously degrade the image contrast and resolution, we give our filters a coating on both sides. This guarantees that the high MTF performance of your lens is maintained exactly as the lens manufacturer intended it. You can also request filters with the new Multi Resistant Coating (MRC) developed by B+W which provides greater durability than the prior multi-coating process.
Finally, most B+W screw-in filters are mounted in a matte black, corrosion-free brass ring, further reducing surface reflections and minimizing distortion or binding of the filter to the lens, even during rapid temperature changes. All filters must pass manual as well as automated tests to insure that each and every one that leaves the factory meets our critical standards.
Here is a page with all their UV filters;
http://www.schneideroptics.com/filters/filters_for_still_photography/uv_&_warming/ 
