Different breeds of hen have different shaped combs: Rose or Buttercup, Walnut or Strawberry, Pea or V shaped. Most ex-bats have a typical single comb with 5 or 6 points. A single comb is the most common type.
Chickens don’t sweat so the comb and wattles are important for keeping them cool in hot weather. This is why you’ll often see ex-bats coming out of their cages with pale, floppy combs, due to the warm environment they were living in.
The dense network of capilliaries act like radiators, letting heat escape into the surrounding air.
Purple colouration can indicate poor circulation and hens with large combs are at risk of frostbite.