Materials have a cost and optional properties, as well as weights for those properties. And stability, which affects the size of the white bar representing the properties. Properties are variable between 0 and 1 as a bar graph. Weights are between the same values and is how much the property resists being changed when the material is combined. A goal material is listed as a bar graph of properties. Grey doesn't matter, red is an area that must be avoided, and green is an area that must be reached. If the white bar of a property is partially in red, or partially out of green, it is unacceptable. Either use more materials or more stabiliser.