I wrote "celui en soie est plus cher" and it was rejected. Is that incorrect? A quick search in google shows that kind of sentence is not uncommon although of course that proves nothing.
It is absolutely correct, but here it is a bit of a short cut compared to the original sentence structure (you skip a verb).
celui que est en soie est plus cher?
"Celui qui est … "
Celle ça fait en soie...?