I agree that a tailor should inform the customer as much as possible practical. but tailors in Hong Kong hate to let customers being knowledgeable according to your statements, in that case they will not tell customers anything unless asked explicitly. I don't think fusing is rubber. It is a fabric or non-woven fabric + adhesive. Adhesive is mostly polyamide based according to one of the producer's website. I am not sure if this is classified as rubber technically.