There are two types of hair: one that moves upward from the scalp and another that lies flat onto the scalp. Let's start with the first type:
Hair Type 1: Up
This type of hair is stiff and tends to grow outwards from the head. Here is an example of what it looks like. It's the kind that puff's out. Below is a variant of this type of hair.
Hair Type 2: Fine
The other hair type lies flat against the scalp, not moving away from the head as the first type. This is how it looks in the example's above. It's the kind that people usually show on those shampoo commercials.
BTW, if you didn't get the idea first, you can mix these two types of hair to get some unique hairstyles.