Abstract: A process for producing composite materials with a metal matrix and with a content of powder reinforcer agent lower than is minimum theoretical compaction value, with said process being based on an infiltration technique, is disclosed, which essentially consists in charging the reinforcer material to a casting mould, and then infiltrating into the same mould the metal matrix in the molten state, with said metal matrix being let cool until it solidifies, and characterized in that the reinforcer agent, consisting of non-metal powders, is blended, before being charged to said casting mould, with a diluting agent having a different compaction degree, constituted by metal fibres and/or ceramic fibres and/or ceramic whiskers and/or metal powders of the same composition as of the matrix.