A collection of all the resourses available in-game.
Each resource has one primary attribute and an associated degree of this attribute. For Aluminum, Copper and Iron they are Malleability, Conductivity and Toughness respectively. All resources within a class have a certain degree of each attribute with their primary being the highest. With this in mind, while crafting and you don't have enough of the resource you need you can use a different one in the same class. The downside of this is that the item crafted has slightly lower quality.