Medium-density fibreboard (MDF/supawood) is an engineered wood product made by breaking down hardwood or softwood residuals into woodfibres, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure.
MDF is generally denser than plywood. It is made up of separated fibres, but can be used as a building material similar in application to plywood. It is stronger and much denser than presswood and should not be compared with presswood at all!
Reference: Wikipedia