The faster moving extruded material buckles and forms {TAIL ~ a corrugated layer} in between {HEAD ~ the two secondary extruded layers} 
The faster moving extruded material buckles and forms { TAIL ~ a corrugated layer } in between { HEAD ~ the two secondary extruded layers }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD