Man's smoking suit, England, 1870s. Silk satin, quilted, with silk cord trim.
The need for smoking caps, and smoking wear generally, arose from the social more of not smoking in front of women, and not smelling of smoke when one returned to their presence.[2] They were often a gift from females, who made them themselves to give to male partners.[1] They were often worn with a smoking jacket, but while the jacket was more or less de rigueur, the cap was optional. Neither was worn by everyone, as smoking was not as popular as it became in the twentieth century,[3] although they could also be worn as part of a man's loungewear outfit with no connection to smoking.
https://en.wikipedia.org/wiki/Smoking_cap