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All mammals have hair, commonly called fur when it's on your cat or koala,

and the thickness of individual hairs varies from species to species.

For example, elephant hairs are more than four times thicker than a strand from an adult human.

Normally when the animal is larger, the hair tends to be thicker.

University of California San Diego Materials Scientist Wen Yang.

She is interested in how biological structures like hair hold up under stress.

That interest comes from a desire to design better synthetic materials.

Yang's team tested the tensile strength of hair from eight different mammal species, including humans.

They subjected those hairs to increasing levels of tension until the fibers broke.

The researchers assume that thick hair, from giraffes, elephants, and boars, for example, would be more robust, but they were wrong.

Interestingly, we find the thinner hair actually is stronger.

In fact, adult human hair was some of the strongest in the study, and children's hair, the

thinnest of all, was even more durable.

Yang's team took a closer look at the hair with a scanning electron microscope. All hair is made of the protein keratin. The

microscope views revealed specific patterns of breakage in the keratin fibers, which are

composed of a protective outer cuticle and an inner cortex that

provide strength.

The microscope images show that the cortex of thicker hair tends to snap when broken,

leaving a clean even break.

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