Jewel thieves and spymasters, take note: If you’re planning a heist that requires you to sneak past infrared security sensors, add a polar bear to your team. Biologists first discovered the animals’ talent for stealth in the mid-1990s. Because the white creatures blended in with the tundra, it was difficult to track them with the naked eye. To solve the problem, scientists tried infrared cameras, but even that didn’t work.

While the cameras picked up heat from the bears’ eyes, noses, and breath, their enormous bodies were invisible to infrared technology. Scientists soon realized the magic was in the fur. The infrared signature of polar bear fur is almost identical to that of snow. Throw in the bears’ big deposits of blubber, and very little heat radiates off of their bodies, rendering them undetectable.

At one point, researchers hoped to mimic the polar bear’s thick fur for defense applications. Specifically, they wondered whether soldiers draped in polar bear hairs would be invisible to enemy night-vision goggles. Unfortunately, ultraviolet cameras are a different story. While the Arctic critters are immune to the infrared, they’re quite visible at the opposite end of the light spectrum—a discovery that shuttered the military’s quest for weapons-grade fur.

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