{HEAD ~ A layer} of {TAIL ~ a resilient and crush resistant polymer} is interposed horizontally at any level through the entire thickness of the material of said elements 
{ HEAD ~ A layer } of { TAIL ~ a resilient and crush resistant polymer } is interposed horizontally at any level through the entire thickness of the material of said elements
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH