If the affected filter was a Kaesemann version CPL, this description comes from Schneider-Kreuznach, who is the corporate parent of B+W...
"To protect the polariser it is either covered on both sides with cellulose acetobutyrate (CAB), known as a Type P film polariser, or it is cemented between sheets of glass, designated a Type KS. ...
The polarisation filters are glued into the mountings so that they are not under stress. The diameter and height of the matt black, anodised aluminium mountings are manufactured to DIN 19030...
Kaesemann polarising glass filters are film polarisers which have been cemented directly between pairs of optically flat, low-stressed glass covers. Appropriate edge sealing keeps the filters secure under tropical conditions and free of haze...
Our filters are resistant to temperatures of up to + 80° C (+176°F), assuming heat is applied over the whole surface and not at localised areas. "
