The mandrel is preferably formed of {HEAD ~ a rigid, foamed plastics material} such as {TAIL ~ a structural foam} 
such as
The mandrel is preferably formed of { HEAD ~ a rigid , foamed plastics material } such as { TAIL ~ a structural foam }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL