Such rear side insulation should have {HEAD ~ a suitably high R value}, such as {TAIL ~ R} 3 to R 15, and can be made either rigid or flexible 
such as
Such rear side insulation should have { HEAD ~ a suitably high R value } , such as { TAIL ~ R } 3 to R 15 , and can be made either rigid or flexible
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH