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