{HEAD ~ The low dielectric constant insulation layer} comprises {TAIL ~ a porous insulation layer}, preferably sandwiched between non porous upper and lower insulation layers 
comprises
{ HEAD ~ The low dielectric constant insulation layer } comprises { TAIL ~ a porous insulation layer } , preferably sandwiched between non porous upper and lower insulation layers
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH