"A three-quarter length jacket worn with a petticoat, the Brunswick was an informal gown or a traveling gown. It had a high neck, unstiffened bodice that buttoned, long sleeves, and frequently had a sack back (loose pleats) and a hood. (See also Jesuit)"
https://www.history.org/history/clothing/women/wglossary.cfm
"A Brunswick gown or Brunswick is a two-piece woman's gown of the mid-eighteenth century.
The Brunswick comprises a hip-length jacket with a high neckline and a hood, worn with a matching petticoat. The jacket sleeves consist of an upper sleeve with flounces at the elbow and a tight, wrist-length lower sleeve.
The Brunswick is one of several informal jacket-and-petticoat costumes popular in the later 18th century, derived from working class costume but made up in fine fabrics.
Originating in France (based on a German fashion), the Brunswick was also popular in England
and the United States as a traveling costume.
Couture Maya's version of the Brunswick/Pet en l'air 2014 as a separate waistcoat with hood and sleeves and jacket
so that the jacket can be converted into a Pet en l'air
http://www.couturemayah.info/eng%20Brunswick.html
"In October of 1771 a London trained Mantua Maker, Margaret Brodie advertises in Williamsburg,
Virginia that she makes Saques, Gowns, Sultanas, Robe de Cours, Brunswicks and Jesuits in the Newest Fashion"
"Based on a sack-back jacket, the Brunswick became popular in the 1760's for travel and informal dress.
Elements included a hood, "gentleman's waistcoat front" and lower sleeves making it a
very warm, verstatile yet comfortable and elegant garment. Recorded in "Barbara Johnson A Lady of Fashion" in
1772 she lists the purchase of "Manchester" (cotton or fustian) checked fabric for a Brunswick."
Burnley & Trowbridge Co. Workshop 2010
https://www.burnleyandtrowbridge.com/westcoastworkshops.aspx
"This garment represents an 18th-century style of jacket known as a Brunswick. A shortened version of the formal sack, the Brunswick became popular in the 1760s for travelling and informal dress. Although this example has a hood, the very fine watered silk suggests it was intended for casual day wear rather than the rigours of 18th-century travel. Some variations have wrist-length sleeves, and buttons at the elbow of this one indicate that it might once have had removable extensions of the sleeve to cover the forearms." 2012
https://collections.vam.ac.uk/item/O115756/brunswick-unknown/
"Derived from a working class ensemble and used as practical outerwear, the Brunswick evolved into fashionable daywear and was then constructed with fine fabrics in the late 18th century. In addition to riding and hunting, they were worn for traveling, walking, visiting, and at home. Stylistically, they tended to follow men’s clothing, signifying their new, less gender specific, role in society. The Brunswick paid homage to fashion trends that traversed economic class."
https://royaldressmakers.wordpress.com/