Oil painting brushes are most commonly made from either natural hog hair, or a synthetic fiber. The hog hairs are stiffer than the synthetic brushes making them better for impasto techniques and leaving brush strokes in the paint. The synthetic brushes are softer and give your painting a softer appearance, as well as being good for more detailed work.
The oil brushes also come in different shapes and sizes. The most common shapes are round, flat, filbert, fan and rigger.
Round brushes hold less paint, but are good for more detailed work and great for thick and thin lines, dabbing on dots and making blotches of colour. They are not suitable for creating hard straight edges. Flat brushes generally have a lot of spring to them and can hold a lot of paint. They are great for the early stages of a painting when you are blocking in large areas. Flat brushes can also be turned on their edges to create fine lines.
Flat brushes are usually available in two lengths of hair - Long Flat and Bright (Short Flat). Brights are better for shorter more controlled strokes. They do not hold as much paint as Flats.
Filberts, are similar to flats, but have a more rounded tip. They give you more control than a bright and will create softer more rounded strokes.
Fan painting brushes are a bit more specialised, it is used for blending colours and is used dry to blend the paint. The brush will begin to loose effectiveness when it becomes more filled with paint.
Rigger are used for delineating fine lines and sharp details.
You can also get long handled and short handled brushes, the heads are just the same, it just depends which you prefer to work with.
After use brushes should be washed in a brush cleaner, this will also help to preserve your brushes. Brushes should always be dried with the bristles facing down and never stood up.