How do cats keep warm in winter and cool in summer?

I am applying the question to domestic cats which can keep cool in summer by staying inside in a cool corner of a room somewhere or the garage or a shed. And they can keep warm using the central heating! Heat pumps and not gas boilers please!!

Norwegian Forest Cat. Tabby-and-white. Photo copyright Helmi Flick.

Colder climates

But at an anatomical level (which is what the question is all about), you'll find that some cat breeds are selectively bred from cats that have adapted to either hot or cold climates. For northern climates you can name the Maine Coon (Boston area and Maine), British Shorthair (UK) and the Norwegian Forest Cat (Norway). 

Their coats are dense with insulating down, which, in cold weather, stands up erect and traps a thin layer of air as double glazing traps air in a wall of warm air between the panes of glass. 

Under the skin is a layer of fat which retains body heat. Heat is lost one third as fast through fat as through muscle.

It is said that in extreme cold a cat will curl up and place its tail over its mouth.

Warmer climates

Breeds adapted to warm climates radiate heat from their bodies more efficiently. The classic breed with the silky, single coat that does this is the Siamese which hails from Thailand, a country with a hot climate. Although you don't see or rarely see Siamese street cats in Thailand which is strange or which makes me question the origin of the breed.

Oriental SH. Photo copyright Helmi Flick. Single-coated beauty.

ASSOCIATED: Single cat coats are better than double coats

Siamese cats lack down hairs. They can shed primary hairs and their blood vessels dilate which speeds up heat loss from the body.

Although cats don't sweat like humans through their skin generally, they do from their paw pads and they pant like dogs when very hot or stressed.  They also lick their fur to deposit saliva on it which evaporates. The latent heat of evaporation removes heat from the body.