A sizer for cooling an extrudate includes a core and a housing. The core includes an extrusion channel which accommodates the extrudate, a core cooling channel, and a core vacuum channel in fluid communication with said extrusion channel. The housing includes a housing cooling channel, a housing vacuum channel, a cooling intake, and a cooling exhaust. The housing cooling and vacuum channels having curved segments. The cooling intake and exhaust being in fluid communication with said housing cooling channel.