Fur, feathers scatter light to keep animals warm

When it comes to protection from extreme temperatures, the polar bear fur is much more efficient than what we can develop for insulating our buildings.

Hairs that reflect infrared light may contribute significant insulating power to the exceptionally warm winter coats of polar bears and other animals, says a study.

Scientists at the University of Namur in Belgium and the University of Hassan I in Morocco were intrigued by the ability of polar bears to insulate their bodies to temperatures of 37 degrees Celsius even during long, cold winters.

The insulating power of the animals' coats made them wonder why thermal insulation in buildings does not work as well, especially when the bears have a layer of fur that is only 5 cm thick, said the study published in the journal Optics Express.

Biophotonics expert Priscilla Simonis, a researcher at the University of Namur, and her team re-examined two of the different ways heat can travel.

Radiation, which transfers thermal energy through electromagnetic waves, and conduction, which transfers thermal energy through the vibrations of neighbouring atoms and molecules.

"Most people assume that fur and feathers keep animals warm primarily by trapping a layer of air that slows thermal conduction. But we suspected that radiation might play a bigger role," said Simonis.

Thet performed a string of experiments in the lab involving a simple computer model consisting of a hot and a cold thermostat that roughly simulated an animal's warm body and the outside, colder environment.

The light scattering properties of animals' coats can have dual purposes, Simonis noted.

"Fur and feathers can generate efficient thermal insulation in the far infrared range while also scattering visible light to produce a white appearance in the visible wavelength range," she said.

This is particularly useful to animals, such as mammals and birds, that live in snowy areas as it provides them with both warmth and camouflage against the white snow.

For humans, focusing on ways to minimise radiative heat loss could lead to the development of new types of ultra-thin insulation.