A material and method for treating timber. The material comprises a preservative and a carrier. The carrier is selected such that it remains mobile within the wood and provides for migration of the preservative within the treated wood. By providing a carrier which is mobile within the wood, the timber has a ‘self healing’ effect wherein the carrier/preservative migrates to any freshly cut or exposed surface of the wood to thereby redistribute and treat such a surface within the preservative and hence maintain integrity of a treatment envelope surrounding the wood.