Engineers compare hundreds of materials at once with a property chart, often called an Ashby chart after the engineer Michael Ashby, who developed the idea. Each material becomes a blob on a map. A classic one has density on the horizontal axis and Young’s modulus (stiffness, introduced in World 2) on the vertical axis.

Both axes are logarithmic. On a log axis each equal step means “times 10” rather than “plus 10”. That is the only way to fit foam (very light and very floppy) and steel (heavy and stiff) on one page, because their values differ by factors of thousands.