Copper is a crafted material which is required for the production of Construction Parts II, Electronics, and Maintenance I. It is created by processing Impure Copper in a Copper Electrolysis with Water, or later game and with better efficiency, with Acid.
As Copper is an ingredient in Maintenance I, which all vehicles and most machines require to prevent breakdowns, a steady supply of Copper is necessary to prevent the potential for the island to enter a death spiral condition.
Below are all the recipes, which contain this item. Note, that some of them may be locked behind Research, and not immediately available in your game.