Abstract: An apparatus and method are provided for generating a foam from a preheated dye solution and subsequently applying the foam to continuous strands of yarn wherein the foam is driven by a pressure differential. The apparatus has a foaming pan for producing the foam from the dye solution and a gas. The pan opens into a foam transmission chamber at or near ambient pressure which fluid communicates with an evacuated spent foam discharge chamber across an open interface. The yarn is dyed by conveying it through the open interface and contacting it with the foam which is drawn across the open interface in a flow path perpendicular to the yarn by the pressure differential between the foam transmission and discharge chambers.