Cinnamon quills are sticks of inner cinnamon bark. These are not the same as the incorrectly named "cinnamon bark" sticks which are actually called Cassia bark (a stronger, more savoury member of the same family).
Cinnamon quills are smoother in appearance and are not hollow. They are easy to crumble and have a more subtle sweet flavour. This type of cinnamon is better for sweet cakes, desserts chocolate & custard.