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