Kolinsky sable hair is one of the perfect brushes for watercolor due to the result of the perfect combination of the best male and female hairs. It is considered one of the best types of hair for its softness and its natural spring. It is also valued in acrylic and oil painting to paint portraits or to finalize details of a piece of work. Brush sizes – The length and width of brushes given shape and size may vary by brand as brush sizes are not standardized. Most fine art brushes are handmade and as such some variation is expected even among brushes from within a single brush line.