Specialised process of transformation of open-cell (hydrophilic – moisture absorbing) foams into hydrophobic foam. The aim of our hydrophobization process is to reduce the surface tension of the material, thanks to which it is not possible to wet it with water. Hydrophobization, however, does not change diffusion of gases and steam, pores remain open and sound absorption properties of the materials are retained. Hydrophobization can be performed in the whole internal structure or on the surface only.