Every picture tells a story. Here is the Simpson Duke Best and an Edwin Jagger Best.
Both have a 23mm knot. One cost £74 and the other was £36. The loft heights are 46mm and 54mm. A good example of a brush with a firm backbone and a floppy.
Density is mainly about the amount of hair in a brush but the firmness of a brush can also be increased by setting a lower loft. Dense brushes tend to be more expensive.