This pet-en-l'air and its ruffle-frill trim is made of pale green linen and lined in cream cotton. It is fastened down the front with hooks and eyes, as well as matching pale green satin ribbon.
This "pet-en-l'air jacket" (as it is called in the collection, though it has also been called a casaquin or caraco) is based loosely on one in Manchester Art Gallery, dated to around 1780-90. According to the gallery description, the original was reputed to have belonged to Eva Marie Veigel, wife of playwright and actor David Garrick.
The original pet-en-l'air has become rather popular online and has appeared on a string of tumblr blogs, including OMG that dress, Historical Fashion and Defunct Fashion. It has also appeared on Fuchsia's 18th century dress blog, where it was called a "little temptress of a very short pet-en-l'air."
The ribbon ties across the front are on the messy side and can perhaps do with being shorter (though this make them trickier to tie). The button-loops at the inner edge of the elbow-length sleeves could also do with adjusting shorter to accentuate the gatherings.
It was rather late in the day when these photos were taken and the bright, yellow light seemed to push it to the side of overexposure.
To commission a similar casaquin in linen or cotton would cost in the region of £50-55.
More photos of the linen pet-en-l'air under the cut.