The force is used to determine {HEAD ~ the density} of {TAIL ~ the insulation}, which, in turn, is used to determine the thermal resistance or R value of the insulation 
of
The force is used to determine { HEAD ~ the density } of { TAIL ~ the insulation } , which , in turn , is used to determine the thermal resistance or R value of the insulation
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH