Abstract: A novel apparatus has been discovered which is of value in the production of polyurethane foam. This invention relates to a one-pass, on-demand apparatus for producing a controlled, homogeneous blend of the polyol-blowing agent mixture used in the manufacture of polyurethane foam using either a low-boiling point or high-boiling point blowing agent. An apparatus is provided to control the amount of each material in the mixture, ensure homogeneous blending of the two materials after mixing, a pressure control means to maintain blowing agents in their liquid state (where necessary), and a monitoring means which allows rapid verification of the operating status of the entire system.