The invention relates to a process for impregnating wood or wood based material. A working solution is preheated to a temperature above the atmospheric boiling point (“a super hot temperature”) above the atmospheric boiling point (“a super hot temperature”) of the working solution, at an elevated pressure sufficient to maintain the working solution in the liquid phase. The working solution is contacted with a wood or wood based material at a super hot temperature and an elevated pressure to cause impregnation of the solution into the wood or wood based material. The impregnated wood or wood based material and any remaining working solution, waste material and/or by-products are then separated.