The blazer began as a jacket worn in boat clubs, for rowing, and was brightly coloured, often striped, with contrasting piping, and single breasted; it was essentially an early sports jacket. At that time, the double breasted, navy blue jacket was known as a reefer jacket. Eventually, as the original blazer became less common, the term come to be applied to the naval version, which gained its modern metal buttons. It is still sometimes called the reefer jacket, and is worn in its original form by some yachting clubs.Blazers!, a thread on the Ask Andy About Clothes forum

Wearing a blazer

The blazer is worn with wide variety of other clothes, ranging from a shirt and tie, to an open-necked polo shirt. It is seen with trousers of all colours, from the classic grey flannel, to white cotton, and brown or beige chinos.

The blazer is now very common in some parts of the world, such as in America, where it forms a major part of business casual wear, and it seen as appropriate for nearly all situations in some part of America.

It is worn as part of school uniform by many schools across the Commonwealth, and in a wide range of colours is still daily wear for most pupils in Britain and Australia. These are blazers in the traditional sense, single breasted often of bright colours or with piping. This style is also worn by some boat clubs, such as those in Cambridge or Oxford, with the piped version only on special occasions such as a boat club dinner. In this case, the piping is in college colours, and college buttons are worn. This traditional style can be seen in many films set in around the Edwardian era, such as Chariots of Fire and Kind Hearts and Coronets.

In the Commonwealth, many regimental associations (veterans' organisations) wear 'regimental blazers' which consist of a blazer with a large representation of the regiment's badge on the breast pocket, usually in the form of a wire badge, and sometimes regimental blazer buttons. In the British army officers do not normally wear badges on their blazers (or boating jackets). Any two regimental blazers will very rarely be the same, as they are made up from different civilian sources and are not issued by any authority. This has come to be representative of the fact that the members of the association are now civilians, but retain the bond that the badge represents. The standard colour is navy blue, although in some associations different colours are worn, such as rifle green for the associations of rifle regiments.

Where the blazer is part of the dress of a school, college, sports club, or armed service veterans' association, it is normal for a badge to be sewn to the breast pocket. In schools, this may vary according to the student's standing in the school; whether a member of the junior or senior school, being a prefect or having been awarded colours. Colours are awarded in recognition of particular achievement in some academic or sporting field.