A new fabric mimics polar bears’ pelts for warmth

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The animal commonly known as the polar bear is called Ursus maritimus in taxonomic terminology. Japanese people call it the "white bear" (shiro kuma to be exact). There are about 26,000 of them currently living in the Arctic and Subarctic regions of Canada, Greenland, Norway, Russia, and the United States. We recognize them easily by their white fur, but these large maritime mammals hold a secret that scientists are discovering and putting to use in the garment industry.

Alaskan polar bear (Wikipedia)

Just how do polar bears keep warm? Temperatures in the Arctic waters are near freezing, and air temperatures are much colder. Researchers in the Department of Chemical Engineering at the University of Massachusetts Amherst studied polar bear skin and fur and designed a fabric to copy properties of their fur for better winter apparel. The first two things to know are that:

• polar bear hairs are translucent, almost colorless, and hollow
• polar bear skin is black

From snowbrains.com

Polar bears are actually covered with two layers of hair. The inner one is soft and dense, and the outer layer has long guard hairs that comprise most of the total body hair thickness. But the hollow center in each hair strand is not empty space. Hollow hairs are similar to those of alpaca, reindeer, and moose, but polar bear hairs are unique. 

Hollow hair showing core (left), larger magnification showing core material (right)

Because the hairs are clear, they reflect and scatter light from the sun. The light bounces around between hairs and even inside individual ones, as the diagram below shows.

Diagram from research by Kattab and Tributsch, 2015

Notice how light bounces and reflects off the hollow center and ricochets between hair fibers precisely with the physics and the properties of glass or plastic optical fibers. Light reaches the dark skin or reflects back and even luminesces (shines) to give the apparent white color of the bear. Researchers Kattab and Trubutsch used colored lasers to measure all of this. We normally think white materials reflect light, but remember that polar bear hair is not white. The black skin under the hair absorbs some of the incoming light and naturally radiates body heat, but the optical properties of the transparent keratin in the hair reflect and trap the heat radiation with the dark skin to keep the animal warm. This process also makes it difficult to use infrared radiation to detect polar bears, because the infrared radiation is trapped under the hair layers.

Dark polar bear skin works with fur to trap sunlight (Univ. of Massachusetts)

The University of Massachusetts researchers adapted this effect to design a material with two layers. The inner layer is made of nylon coated with a dark polymer called PEDOT, which is an excellent conductor of heat from light sources. To simulate the polar bear's hollow hairs, they added on top of the PEDOT a layer of transparent polypropylene threads that channel visible light down to the PEDOT. The new material is 30% lighter than cotton, too, and better at keeping the wearer warm. Direct sunlight is not needed to absorb energy as heat, so this can be used even on cloudy days. The University of Massachusetts researchers have coined the phrase "on-body greenhouse effect" to describe this material's function. The company Soliyarn, Inc. has already begun manufacturing this.

The material is not just good for retaining heat for the outdoors sporting industry. The material is touted at being useful for anyone working in the cold, whether they are conducting military operations or they simply have arthritis. Certain derivatives of PEDOT are also currently being investigated for use as wearable sensors for muscle and heart conditions, in a field known as "smart technology".

 

If you want to see a short (less than 2 minutes) video showing how polar bears can be white, gray, red, or even green, go to this link.