wherein during the initial expansion, {HEAD ~ the foam material} expands between {TAIL ~ the coils} of the helical spring, and within a gap provided between the spring and the housing 
wherein during the initial expansion , { HEAD ~ the foam material } expands between { TAIL ~ the coils } of the helical spring , and within a gap provided between the spring and the housing
OTH OTH OTH OTH OTH OTH 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