Photos of pajamas as outerwear in Shanghai.
The prevalence of pyjamas, Guariglia explained to me, was due to both the extreme summer heat and the lack of plumbing. Most Shanghaians share outdoor communal toilets and thus the boundaries of what was considered one's home have expanded past people's houses to the public bathrooms. Once that relaxation of the dress code became acceptable (starting around the 1980s) the perimeter for p.j.-wear just kept expanding until many people were wearing them day in day out.