An old-style oil paintbrush typically consists of a bristle brush with long or short handles. The bristles are made from boar hair, which is known for its stiffness and durability. The brush is designed to hold and distribute oil-based paints effectively.When using an oil paintbrush, the bristles pick up the oily pigments from the paint and allow you to apply them to a canvas or other painting surface. The brush bristles are usually thick and dense, allowing for good color retention and smooth application.