A method may include determining a first dry mass flow rate of a wet paper material stream based on a first amount of contaminants, a first moisture content, and a first wet mass flow rate of the wet paper material stream, determining a second dry mass flow rate of a wet plastic material stream based on a second amount of contaminants, a second moisture content, and a second wet mass flow rate of the wet plastic material stream, calculating, using the first dry mass flow rate and the second dry mass flow rate, a paper/plastic ratio of a combined stream of the paper material stream and the plastic material stream, and adjusting, a flow rate of paper into the paper material stream and a flow rate of plastic into the plastic material stream such that the calculated paper/plastic ratio of the combined stream equals a target paper/plastic ratio.