Dị ka ihe ọhụrụ nkwakọ ngwaahịa nkwalite, anyị akụrụngwa bụ ọhụrụ nkwakọ ngwá ọrụ e mere na arụpụtara na-adabere na àgwà nke kpo oku shrinkage nke nkwakọ ihe nkiri.Ọ nwere ike ịhazi otu ngwaahịa (dị ka karama PET) na-akpaghị aka, gbakọta n'ime otu, ịkwanye servo karama, kechie ihe nkiri servo, wee mepụta ngwugwu setịpụrụ mgbe kpochara, na-ebelata, jụrụ na imecha.