>>853
https://www.daviesandson.com/playing-by-the-rules/
Oddly, the grey- or black-striped pattern of the trousers are called cashmere stripes.
This not a reference to the luxurious fibre but more likely a throwback to the late 1700s when cassimere or casimere fabrics were woven in England to emulate the cashmere twills imported from India.

https://en.wikipedia.org/wiki/Frock_coat
On more formal outings the coat was worn with a pair of cashmere striped morning trousers: (cashmere stripes refers to the muted design in black, silver and charcoal grey, not the fibres of the cloth.)

わざわざ素材がカシミアというわけではないと明記してある
cashmere stripesの語源の有力な説は上にある通り

>>853の主張の根拠はどこかな？

カシミアでモーニング仕立てるのは拘ってるんじゃなく単に高額な生地を使いたいだけだろう
スパンカシミアの服地が実現したのはいつの時代だと思ってるんだ