{TAIL ~ the material} of said intermediate flat portions and said corrugations having {HEAD ~ substantially the same thickness}, 
{ TAIL ~ the material } of said intermediate flat portions and said corrugations having { HEAD ~ substantially the same thickness } ,
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH