A quality paint brush will have hairs that form a point and have a good spring to them - they bend while painting but return quickly to their original shape. A good brush will also hold lots of paint and deliver that paint evenly throughout the stroke. Brushes usually have a number to indicate their size - the larger the number, the larger the paintbrush. The larger the brush the wider the line that can be produced, although with a light touch a fine long line can be made because of the pointed nature of the brush.
The best brushes are made from natural hairs, although there are brushes made from a combination of natural and synthetic materials which are adequate.
Sable hair brushes are considered to be the best for painting. The hair comes from a variety of pine martin and the Kolinsky sable from Siberia is considered the best. These brushes are more expensive than others, but are soft and flexible, hold their paint well and can make an expressive thick to thin line.
Ox hairs are normally used for making rigger brushes. This is a round brush with long hairs, said to be used to paint the lines of ships' rigging in the past. The hair is strong and springy making it useful for long lines and thicker paints.
Squirrel hair brushes are useful for applying paint in broad, thin layers for matting.
Goat hair brushes are normally known as hake brushes. These are a traditional, oriental style brush. It lacks spring, but forms a good point and so is useful to cover larger areas quickly with a gentle touch.
Pony hair is made into short round brushes used as soft stipplers.
Hog hairs are made into hard, very economical brushes. They come in flat and round shapes. They are most used for stippling and can be trimmed, shaped, used, and abused for years.
Badger hairs are thicker at the end and thinner at the root, creating a conical shape. These soft brushes are used to blend paint once it has been spread on the glass. The brush is swept across the surface of the paint to blend or move paint and remove stroke lines.