It is unlikely that any fabric can be rendered permanently mildew-proof under all conditions. “Mildew-resistant” is a more proper term. Usually refers to a treatment on a cloth with various non-toxic chemical compounds that poison or discourage the growth of mould and fungi. Effectiveness is directly proportional to the type of fungicide and the quantity of fungicide contained in the finished cloth (to the point of maximum potency). The treatment may be durable or non-durable.