Sorry, but the legal training in me wants to respond. I would see the issue this way:
If a design’s function cannot be removed from the aesthetics then it cannot be copyrighted. The fact that the function of the seat is to have a person sit in it, bars this item like other functional items (desk, table, etc.) from being copyrighted for its design because the function of its design is to support a person sitting and that cannot be removed from its aestheics. The ergonomics of this chair which wrap around a persons body’s could be a point of contention because one could argue that it is a removable aesthetic that has no function, but allowing a chair to curve or cup a humans back, shoulders, buttocks, and legs–or impressions of the human body–could be barred because: (1) it has a function because it is an ergonomic design (building products that conform to the human body to provide better comfort and function), and (2) because there are only so many ways to sculpt the back of a humans body, so allowing someone to have the copyright of that design would stymie innovation, thus a copyright would also not be allowed or would be contestable. So most likely a copyright of this design would not be available.
Patents however are a different issue. In some states, direct molding of an item is not considered reverse engineering (which is the way around some Intellectual Property law) and it would be barred. So in those jurisdictions, if he is subject to them, this would illegal if he was planning on selling it. However, my question would be: (1) is there a patent?; and (2) is this person planning on distributing? If the answer is yes to the first, I would still argue that a person making a copy of a product to recreate it in carbon fiber or another composite form–even if that product comes in carbon fiber-- would not be stealing. For instance, perhaps he has one seat and wants to build another so that he has two seats that remain in his possession/ownership. As long as he is not selling or distributing, then he is not harming the producer. This reminds me of the legal cases that surrounded VCRs. The tv and movie companies argued something similar, but essentially saying that it was stealing because people were making unauthorized copies of their work; however, the US Supreme Court decided against them, finding that if it was for personal use then it could be allowed because preventing it would stymie innovation. For as long as it was not being distributed or sold, it did not hurt the creators interests. This particular ruling allowed us to not only have VCRs and other recording devices, but eventually lead to Tivos and DVDRs. I would believe that this is exactly how they would view an unauthorized reproduction for a hobbyist. If no patent exists and there is no distribution, I would argue the same thing, except in this scenario the creator has zero claim to stop the unapproved reproduction.
Still, I would argue that this project is no different from the 99% of all composite products that hobbyist build that have zero adaption or modification of a product’s original shape or design. Most products that people build for hobby, are standard direct molding–take a part, make a mold, make a new part. We see this constantly whether it be a motorcycle fairing, a cello, guitar, rc car lexan body , etc.; people take another persons design and build it in a composite material.
I sympathize and respect your feelings on the matter as I’ve been in the same situation with people copying products of mine, but I think the legal issues for this particular product are tricky and if the person is not planning distribution then it is not harming the creator.
So that’s my two cents.
