A method of improving gas, water, water vapor, and/or grease resistance of a porous material is disclosed which comprises treating th(e material with a wax, poly(vinyl alcohol), plasticizer, and optionally a polyamine. In some embodiments, an optional first treatment agent may be applied to the material prior to the application of wax and poly(vinyl alcohol), plasticizer, and optionally a polyamine. Materials that have a single coating of wax, poly(vinyl alcohol), plasticizer, and optionally a polyamine, as well as materials having a multi-layer coating that includes a first coating of a first treatment agent and a second coating of wax, poly(vinyl alcohol), plasticizer, and optionally a polyamine are also disclosed.