Barbour recommends that you re-wax a jacket at least once each year with their Thornproof Wax Dressing (https://www.outdoorandcountry.co.uk/barbour-thornproof-dressing.html) to preserve its weatherproof qualities. Depending on the amount of use the jacket gets, and how it is stored, this may need to be increased. If you notice that there are dry patches appearing on the jacket then you should treat these areas immediately, once the wax starts to dry out all over the jacket, it should be fully re-waxed.