An article on FX Guide (thanks to Phil Nolan for the link!) goes over the incredible amount of work necessary to make the heroine's hair look just right. There are 1,500 individual curls on Merida's head. 1,500! Each one had to manipulated just so. The hairs had to move with the character and look natural. I knew it was a difficult task but until I read details, I had no idea what it took to make that much animated hair look right and beautiful.
It goes into great depth about construction, styling, and movement and is full of information such as this:
“Over the course of doing her hair,” comments Pixar simulation supervisor Claudia Chung, “one thing we noticed was that the idea of weight of curly hair defies logic. If you took a curly hair and weighted it and then one took straight hair and weighted it, with the same weight in mass, the way each would react to gravity is quite different.”And some videos, including this one showing how the layers of hair build up:
Again, you can read more at FX Guide. Do not read if you haven't seen the movie yet though; there are lots of plot spoilers in that article.