Magnificent! This is vintage Bonaaru - a Japanese brand. As one would expect, the attention to detail is utterly superb.
The label is in Japanese so can't read it (sadly!) but I am pretty certain it's cotton.
A good fit for a UK8 - small UK10. If you're broad shouldered then it will be too tight for you across the back... so small to mid shoulders only :-).
Sits on the knee in length (based on a height of 5'7")
Has an elasticated waist.
In excellent condition.