I also watched this, a very enjoyable documentary. I particularly liked their experiments with the 20's kit. It mentioned the jackets and trousers were made from garbadine which I think is essentially Ventile?
From wiki,
Gabardine was invented in 1879 by Thomas Burberry, founder of the Burberry fashion house in Basingstoke, and patented in 1888. The original fabric was water-proofed before weaving and was worsted or worsted/cotton, tightly woven and water-repellant but more comfortable than rubberized fabrics.[3] The fabric takes its name from the word "gaberdine", originally a long, loose cloak or gown worn in the Middle Ages, but later signifying a rain cloak or protective smock-frock.[4][5]
Burberry clothing of gabardine was worn by polar explorers including Roald Amundsen, the first man to reach the South Pole, in 1911, and Ernest Shackleton, who led a 1914 expedition to cross Antarctica. A jacket made of this material was worn by George Mallory on his ill-fated attempt on Mount Everest in 1924.[6]
