Essay: Wizard Clothing
Rowling writes about standard Wizarding clothing, which she notes harkens back to another era, and about the laws and other factors which affect how well witches and wizards manage to fit in with Muggle clothing.
Interesting facts and notes
From the International Statute of Secrecy:
“When mingling with Muggles, wizards and witches will adopt an entirely Muggle standard of dress, which will conform as closely as possible to the fashion of the day. Clothing must be appropriate to the climate, the geographical region and the occasion. Nothing self-altering or adjusting is to be worn in front of Muggles.”
"Standard wizard clothing comprises plain robes, worn with or without the traditional pointed hat." Not coincidentally, this describes the required dress at Hogwarts perfectly.
Archie Aymslowe, mentioned as the president of F.A.R.T. and proponent of wearing robes could very well be the Archie the trio encountered while queuing to get water at the Quidditch World Cup campground on Dartmoor. It does sound like him ...
A fringe movement calling itself Fresh Air Refreshes Totally (F.A.R.T.) insists that Muggle trousers 'stem the magical flow at source' ...
Arriving at Diagon Alley