PACaMAC backgrounds

From Wikipedia:

The Mackintosh or Macintosh (abbreviated as mac or mack) is named after the Scottish inventor, Charles Macintosh of the raincoat fabrics, though a letter k is added by many writers.

Charles Macintosh patented his invention for waterproof cloth in 1823 and the first Mackintosh coats were made in the family's textile factory, Charles Macintosh and Co. of Glasgow. Early coats had problems with smell, stiffness, and a tendency to melt in hot weather, but Hancock further improved their waterproof fabrics, patenting a method for vulcanizing rubber in 1843, which solved many of the problems.

An anorak or cagoule, cagoul or kagoule (from the French cagoule meaning hood) which can be rolled up into a very compact package and carried in a bag or pocket was invented by Noel Bibby of Peter Storm Ltd. in the early 1960s. It has an integral hood, elasticized or drawstring cuffs, and a few poppers or a short zip at the neck. It does not open fully at the front and must be pulled on over the head. In some versions, when rolled up, the hood doubles as a bag into which the rest of the coat is pushed. It became very popular in the United Kingdom during the 1970s.

The PACAMAC is a foldable  and is the British English term for a lightweight (usually without lining), weatherproof anorak with a hood,. In North America and Japan cagoules are more commonly known as windbreakers.

Remark: Although the Mackintosh style of coat has become generic, a genuine Mackintosh coat should be made from rubberized or rubber laminated material.

So today we say PAC-a-MAC, short for 'pack your Macintosh'