Abstract: A venturi for producing medium expansion foam for use in fire fighting applications. The new venturi contains a swirl inducer bushing near the entry of the nozzle, a two section frustum shaped diffuser, and a plurality of angularly oriented air injector openings. The venturi progressively decreases in cross-sectional area from a discharge point thereof to a throat of the nozzle. The cross-sectional design together with orientation of the air injector permits high quality lasting foam to be produced under a broad fluid supply pressure while minimizing the amount of foam reagent employed.