joining the channels in each array creating a plurality of layered wall segments separated by ridges if desired the innermost and or outermost layers may be thicker than any intermediate layers present providing increased toughness and strength the channels are coated with silicone oil or other low friction substance such that the layered segments are slip layered segments which readily slide relative to one another as described above this ridged balloon is a strong soft medical balloon in which ridges and slip layered segments provide differential stiffness about the circumference of the balloon for improved foldability additionally the ridges anchor the layers to one another providing easier joining of the balloon to the catheter while coextrusion is generally the preferred method for forming the ridged balloons it is also possible to extrude tubes having the channels already formed therein using a known type of extrusion die however the thickness of the channels within the blank is extremely small typically about 0 025 0 5 mm within a tubular balloon blank having a total wall thickness between about 0 07 and 1 0 mm and outside diameter between about 0 25 and 5 0 mm therefore extrusion with the desired preformed channels can be more difficult than coextrusion and coextrusion is generally preferred the foldability and surface characteristics of any of the balloons described herein and particularly of the ridged balloons may be improved by.