A bed jacket is a short and usually pretty lingerie top worn in years gone by to keep a woman warm while sitting up in bed. She may have been ill, she may have recently had a baby, or perhaps her husband was bringing her breakfast in bed. Remember, in those days houses didn't have central heating and would have been cold. Bed jackets were also worn for modesty, when receiving visitors while ill in bed, or in hospital having just had a baby. Some bed jackets are warm, woolly numbers worn in winter - brushed nylon was very popular in the 1960s. Others are feather light silk or rayon, often embroidered or lacy. Smocking and quilting are also often seen on bed jackets.
These days, a bed jacket of the lightweight and pretty type can look great worn as a summer jacket or cover up. A knitted or nylon bed jacket can still come in very useful in hospital.