A method of mixing two or more materials, at least one of which is supplied in packaged form comprises the steps of passing the packaged material to a processing unit while still in its packaging and then breaking open the packaging in the processing unit so that the material can escape therefrom. The materials can then be mixed in a mixing apparatus, with the broken down packaging subsequently being filtered from the mixed materials. In this way the material which is supplied in packaged form need not be handled directly. The filtered out packaging may be washed prior to disposal or recycling.