introducing an expandable liquid foam material inside of the housing and allowing {HEAD ~ the material} to expand forming {TAIL ~ a compressible foam} that is compressed and expanded when the helical spring is compressed and expanded 
to expand forming
introducing an expandable liquid foam material inside of the housing and allowing { HEAD ~ the material } to expand forming { TAIL ~ a compressible foam } that is compressed and expanded when the helical spring is compressed and expanded
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH