Rubber is a Crafted material available from the start of the game. Rubber is an insulator used in the production of Electronics in combination with Copper conductor in a Rubber Maker. It can be crafted from Diesel, Ethanol or Naphtha combined with Coal or Sulfur.
Rubber is required for conveyor belts and Vehicles created in Vehicle Depot.
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.