Blown oils are produced at elevated temperatures by blowing air through the oil. The oil polymerises by cross-linking across the double bonds but in this case there are oxygen molecules incorporated into the cross-linking bond. Peroxide, hydroperoxide and hydroxyl groups are also present. Blown oils are also known as oxidised, thickened and oxidatively polymerised oils. Both types are, generally, manufactured to viscosity specifications.
Blown oils may be produced from a wider range of oils than stand oils. In general, blown oils are darker in colour and have a higher acidity when compared to stand oils. Because of the wide range of raw materials used, blown oils find uses in many diverse industries, for example blown linseed oils are used in the surface coatings industry and blown rapeseed oils are often used in lubricants.