wherein each of the two pieces of the mold insert comprises {HEAD ~ at least one portion} partly defining {TAIL ~ said mold cavity} which is made of a material or a combination of materials, other than glass the thermal diffusivity α of which fulfills the condition 
partly defining
wherein each of the two pieces of the mold insert comprises { HEAD ~ at least one portion } partly defining { TAIL ~ said mold cavity } which is made of a material or a combination of materials , other than glass the thermal diffusivity α of which fulfills the condition
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL 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 OTH