Abstract The present invention relates to a preservative formulation for use in treating wood or other cellulosic materials, said formulation comprising: at least one biocidal metal compound; at least one preservative; and an aqueous carrier, wherein the preservative formulation has an uptake in the sapwood of less than about 220 L/m3 yet achieves substantially full penetration of the sapwood. Preferably, the preservative formulation is copper/tebuconazole in a ratio of about 25/1 w/w; and the wood is around 25 mm in thickness - for instance, decking timber.
