With 300,000 hairs per square inch, northern fur seals have the second thickest fur on the planet.

Here at the New England Aquarium, the resident fur seals are special members of our community, but a little-known fact is that these marine mammals are also helping scientists make incredible discoveries.

A lecturer and engineer at the Massachusetts Institute of Technology (MIT), Dr. Alice Nasto studies the interaction between fluids and hairs in animals. A few years ago, she came to the New England Aquarium to study the physics of fur seal hairs as part of her Ph.D. work. Nasto wanted to understand the secret behind these hairs’ unique, insulating structure in the hopes of applying nature’s designs to innovative materials. 

northern fur seal fur
Dry fur seal hair

“We hoped that our research could inform technological advances and inspire the design of new textiles with advanced water-repellent features, such as novel wetsuits, in which staying warm and dry is paramount,” Nasto said.

Seals have two layers of barb-like hair: a visible outer layer that is comprised of long, dark hairs and an inner, down-like layer of underfur. Referred to as “guard hairs,” the outer hairs keep the inner layer warm and dry. The hairs have a barbed structure that helps them stick together, seal in air, and heat. At the Aquarium, Nasto got a firsthand look at this structure. 

“It’s difficult to grasp a full understanding of fur properties and the seal’s grooming habits from simply reading scientific journal articles,” she said. “It was really fascinating to see the seals up-close and to look at samples under a microscope.”  

fur seal fur
The two layers of fur seal hair (Photo: Alice Nasto)

Back at MIT’s labs, testing began. Inspired by her observations at the Aquarium, Nasto fabricated artificial hairy surfaces to emulate fur seal hairs. By submerging the mold in liquid at precise speeds, Alice and her team were able to observe how the hair spacing, length, and speed influence air trapping.

“The denser and the longer the hairs are, the dryer or the more water-repellent the hairy surface is,” she explained.

Nasto fabricated artificial hairy surfaces to emulate fur seal hairs. (Photo: Felice Frankel)
Nasto fabricated artificial hairy surfaces to emulate fur seal hairs. (Photo: Felice Frankel)

Among other topics, Nasto has since studied the mop-like nature of bat tongues. While her research extends far beyond the marine world, she is very grateful for the different seals she met along the way.

“My visits to the Aquarium were really essential to fully grasp these facts through firsthand observation and conversations with all the trainers,” Nasto said.