The term structural foam refers to a body with {HEAD ~ a low density cellular core} which has {TAIL ~ a solid integral skin} 
has
The term structural foam refers to a body with { HEAD ~ a low density cellular core } which has { TAIL ~ a solid integral skin }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL