Answered by Shaykh Faraz Rabbani
I would like to know if I am allowed to wear a jilbab made of jeans fabric, or if it would be “imitating the unbelievers” somehow, and so prohibited or disliked.

Walaikum assalam wa rahmatullah,
Unless you intend to be like disbelievers, it would not be disliked to wear denim clothing (such as a jilbab for women, or loose jeans), if it fulfills the conditions and proprieties of modest Muslim clothing.
And Allah alone gives success.
Wassalam,
Faraz Rabbani