Question: My hair is very thick and somewhat layered. I am letting it grow out to shoulder length. At the moment the sides are jaw length and tapered back to the base of my neck. I want to wear it so there is volume and that it's somewhat curled under at the ends. What size curling iron should I buy?
Answer: It sounds like you need a round brush! They are great for creating volume and adding a little bend to your ends. Additionally, using a blow dryer is less damaging to your hair than using a curling iron on a regular basis. There is a bit of a learning curve when you start round brushing your hair but it's surprisingly easy once you get the hang of it. Check out my tutorial to learn.
Because your hair is shorter, you'll probably want a smaller round brush. A 2 or 2 1/2 inch brush should do the trick and because your hair is thick, I think a ceramic barrel brush with plastic bristles would be best. To learn all about brush types and materials, check out this post.
If you are set on a curling iron, I'd try a 1 1/2 or 2 inch barrel ceramic iron like this one. This curved flat iron would also work, depending on how much bend you want on the ends. For more help choosing an iron, please refer to my post on curling iron materials and construction.by