One side or both sides of the panel 20′″ may be covered with {TAIL ~ a layer}, such as {HEAD ~ an outer covering layer} 
One side or both sides of the panel 20′″ may be covered with { TAIL ~ a layer } , such as { HEAD ~ an outer covering layer }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD