The make-up of the network was changed to include mostly fibre-to-the-node after a new government was elected in 2016. This has led to an increased need for copper wires.
In Senate Estimates, the government said, in response to questions that were 18 days overdue for answers, that NBN Co had purchased 15,051 kms of copper to date, from a company named Prysmian.
The copper is being sourced from Brazil and Turkey, apart from Australia.
"The total purchase of copper will vary with final rollout technology mix, as each technology has unique characteristics that affect copper cable utilisation," the questioner was told.
Referring to this, Labor shadow communications minister Michelle Rowland said that the use of taxpayer funds on "last century's copper" was another indictment of Malcolm Turnbull's "failed second-rate NBN".