The calendar may say spring, but the thermometer is dipping mighty low overnight lately.

While I’m burrowed into my covers like a vole in a lawn, Joey sleeps curled up in the center of his nest, surrounded by cold air. How does he keep warm?

It turns out his coat is designed for more than just good looks.

A dog can have a single coat (one layer of the same kind of fur) or a double-coat (two-layers of two different kinds of fur). Double-coated dogs have a soft, insulating undercoat that protects a dog against both cold and heat. Stiffer, longer guard hairs work to direct snow or water away from the undercoat and skin. Oil glands in the hair follicles keep skin and fur supple and smooth and also help water run off the hair and away from the skin. (Spaniels and other dogs bred to work around water tend to have oilier coats than other breeds.)

VIP Fibers, a company that spins dog fur into yarn — Yes, Virginia, there really are dog fur spinners — suggests that unless you live in a really, really cold climate you not make entire garments out of dog fur yarn because it’s up to 80% warmer than sheep wool.

A major reason why Joey can be comfortable and warm in my cold room overnight is that dogs have muscles under their skin that allow them to raise their fur.  This traps a layer of air between the warm skin and the cold night hair.  (It’s similar to the goosebumps we get when we’re cold.)

Curling into a ball with his paws tucked under his belly and his tail wound around over his nose keeps an envelope of warmth around him as he sleeps.

This system is so effective that samoyeds, sled dogs and other dogs that live and work in arctic regions lose very little body heat even when sleeping on snowing in freezing temperatures. According to Ted Greenlee, a samoyed owner who moved his dogs from the Pacific Northwest to Florida, this insulating effect works against heat in much the same way as it does against cold. he says that well insulated dogs such as his samoyeds adjust better to heat than short-haired dogs that don’t have an heavy undercoat — as long as they have an effective way to get rid of their own excess body heat.

I can relax under my comforter now knowing Joey is cozy inside his perfectly designed coat.