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