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