Kelly's Cork Sealer helps seal and waterproof Birkenstock cork surfaces, as well as helps prevents cracking and flaking. Michelangelo recommends applying cork sealer to your Birkenstock sandals twice a year, in May and in September. This product goes on white and dries clear. Be careful not to over apply or it will have a milky finish after drying. Thinner coats are better than thicker coats. Cork sealer DOES NOT go on the suede leather top covers.