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