Hair for dolls
I use just natural fibres for my dolls' hair. I tend to buy them from Etsy sellers who cut their own llamas, alpacas and goats and are cruelty-free. Natural hair of these animals is so silky, fine and smooth! Also, you can dye them and style using heat. I know that there are a lot of doll artists who do amazing wigs for dolls using synthetic hair but I had no luck finding something that would look as great as natural fibres.
Goat mohair
Very fine and silky hair with loose curl. Since I started to make porcelain dolls, goat mohair is my go-to fibre for dolls. You can find very long locks so that's a huge plus! Have in mind that this is goat fur so even when you buy combed and washed locks there's still some distinctive smell so you'll need to wash them with shampoo a few times before using.
Where to buy:
Suri alpaca
Very similar to goat mohair but usually doesn't have that beautiful loose curl. Because of that, it works very well for straight hair wigs. You can style the hair using the heat and make them incredibly straight, shiny and smooth. You might need to wash the hair a few times even if you're buying washed and combed locks. I find that it has less smell than goat mohair.