SnoSeal or any other beeswax type topcoat treatment. If they werent lined I say use PURE Neatsfoot Oil (NOT the 'compound') and topcoat with the SnoSeal. After each wetting of the boots they need to be slow dried (I have one of those PVC 'boot driers', but used to upside down them over the hear register at the far end away from the furnace), then retreated. I have some boots over 20yrs old that that stood the test.