Furry Funnels

Are polar bears really white?

Polar bears are white because that is nature's way of camouflaging them in the snowy Arctic. Right? Not necessarily, says a scientist at the U.S. Army Research and Development Command in Natick, Mass. After studying the furry beasts, Physical Chemist Malcolm Henry finds that polar-bear hairs are really transparent and only appear to be white. What is more, he says, man can probably benefit by copying this peculiar characteristic.

Henry became bullish on polar bears quite accidentally. After reading in National Geographic about the work of the University of Oslo's Nils Oritsland, Henry was surprised to learn that aerial infrared photography, sometimes used to count populations of wild animals, is of no use in tallying baby harp seals or polar bears. Neither of the species register on the film because their external temperatures are virtually the same as that of the cold polar ice around them. More remarkable still, even though both the bears and the pup seals look white to the eye, they show up much darker than the background ice and snow in ultraviolet (UV) photography. Somehow, even though white objects are excellent light reflectors, the animals' bodies absorb virtually all the solar ultraviolet rays that hit them.

Already involved in a project to develop new ways of keeping soldiers warm in the Arctic, Henry decided to find out how the polar bear accomplishes this feat. That was not easy; zookeepers repeatedly rejected requests for a few tufts of polar-bear hair, pointing out that the formidable beasts did not take kindly to plucking or barbering. Finally, a Canadian colleague provided a pelt. The hairs were examined with a scanning electron microscope, which revealed that they were hollow, like tiny tubes, and contained no pigment whatsoever; they appeared white only because their inner surfaces were rough and, like transparent snowflakes, reflected visible light.

Henry and his colleagues, John A. Sousa and Northeastern University's Richard E. Grojean, concluded that the polar bear's hairs are really miniature light pipes, funneling only ultraviolet light down through its hollow core. If that is indeed how the polar bear traps warming UV, humans may be able to do the same by using a synthetic version of its fur for cold-weather clothing. The Department of Energy, for its part, hopes that similar light pipes may some day be incorporated into solar energy collectors far more efficient than any that exist today.

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