a melt distribution block for a co - extrusion die has a generally annular body , for example in the shape of a conical frustum . the annular body has opposed front and rear faces and opposed inner and outer faces . inlets at the outer face have channel ports for accepting flow of melted polymer into the distribution block . flow controlling valves independently control the flow of the melted polymer through each of the channel ports . melt flow channels on the front and rear faces between the inner and outer faces are in fluid communication with the channel ports . a thermal insulation layer within the distribution block between the front and rear faces separate all or part of the melt flow channels on the front face from all or part of the melt flow channels on the rear face . such blocks together with separator blocks may be axially stacked front to rear around a central mandrel to form an extrusion die suitable for making blown films into tubular form .