Thank you for your interest in the Isola Dining Side Chairs, in Weathered Finish, Set of Two (154169_WEA). The frame is teak. Treating teak with oil or teak sealer helps to retain and enhance teak's natural golden honey color. It does not affect its strength or longevity. Teak that remains outside for extended periods of time will require re-oiling or re-sealing approximately every 2 to 3 months and should be kept out of direct sunlight. Tung oil is recommended by professionals, but linseed oil and store-bought teak oil can also be used. (If using a commercial teak sealer, follow the manufacturer's instructions).