We know that bones provide a framework for our bodies, protect our vital organs, and facilitate movement, but what makes them strong enough to perform all of these important functions? In a clip from the BBC’s Bang Goes The Theory: Series 8, Brit Lab host Liz Bonnin dirties up a junkyard while answering the all-important question: what are bones made of?

All 206 of our bones are constantly changing shape and composition to meet the body’s needs. To do so while being strong enough to withstand over 1 ton of compressive force, bones have to be made up of some pretty unique materials. One of those materials is collagen, a protein that provides the softer, flexible framework for bones. The other material is calcium phosphate, a mineral that strengthens the framework.

If our bones were only made of collagen, then our bodies would have no stability. Vice versa, if our bones were only made of calcium phosphate, then they would fracture under even the slightest amount of pressure. The combination of collagen and calcium phosphate make our bones flexible and strong enough to withstand all that pressure.

According to the National Institute of Arthritis and Musculoskeletal and Skin Disease, more than 99 percent of our body’s calcium supply is found in our bones and teeth. There are essentially two types of bone in the human body: cortical, which forms the tough outer layer, and trabecular, which makes up the spongy inner layer.