n A special type of capillary rheometer developed by W. Kostyrzewski to measure the density and viscosity of foaming polyurethane immediately after mixing. Creaming time is also measured. It consists of a three-section, vertical acrylic tube, adapted at the bottom to a reaction–injection–molding mixer (RIM machine). The bottom chamber is large enough to contain the mix charge delivered by the RIM machine, and the mixture rises through an instrumented and temperature-controlled “capillary” as the foam forms and expands. The instruments are connected to an analog-to-digital converter and computer. The foam passes up through the capillary into a larger-diameter collection chamber and raises a floating disk that can be weighted to adjust the pressure on the foam as it rises. Flow rate is inferred from foam density; rate of change of density, and shear rate at the capillary wall are computed from flow rate. Shear stress is inferred from the pressure–transducer readings.