LEE Resin filters are made of an optical polycarbonate resin, and should be treated as you would a lens, or a pair of spectacles. Clean with a lint free cloth for general use, and if necessary a lens cleaning solution to remove greasy fingerprints. Salt spray should be dissolved in warm water (not hot) and the filter dried and cleaned as usual.
LEE Filters have developed our own cleaning solution - ClearLEE. You can find further information on this on our accessories page here - LEE100 Accessories - LEE Filters