An applicator for applying foamed treating liquor across the flat width of a traveling textile fabric or like substrate includes an arcuate housing having an arcuate interior partition wall intermediate a foam inlet port and a foam emission nozzle opening in the housing to define a distribution chamber providing a turning foam pathway from the inlet port about the curved edge of the partition wall to the emission opening. The curved edge of the interior wall is parabolic in shape to define substantially all possible foam flow paths from the inlet port linearly to the curved edge and linearly the respective shortest distances therefrom to the emission opening to be of substantially the same total length. Accordingly, foam residence time within the distribution chamber is substantially constant regardless of the flow path assumed, to control foam degeneration to occur uniformly for uniform widthwise treatment of the traveling fabric.