It seemed Prop Shop 3D printed everything including parts on the light sabers. I'd bet, although I have no direct knowledge, that the helmets were 3D printed as it seemed that's what they knew how to do and they had those huge 3D printers. We would have to go back and watch their behind the scenes videos again to see if the helmets besides Vader were shown being molded or made any other way. Only the insiders at Prop Shop really know the truth.
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Looking at that last video, things that can be assessed
First off- Bowcaster- He says the main body is 3D "PMMA" Printed, the main bar is aluminum (you can see 2 unpainted ones sitting on the shelf to the left, which do appear metal). He states some other components are 3D printed or laser cut. Those domes you see, I'm not sure if he specified, but you can see both painted and unpainted ones on the same shelf w/ the aluminum bowcaster bars, which the color of the unpainted domes (seen in white/cream color) could go either as cast resin OR 3D printed. Later in the video when he's talking about Ray's staff, you can see an unassembled bowcaster and see the Scope pieces clearly in metal.
Rey/Luke ESB style saber- You see the dude working on them. Those clearly look to be metal pieces. I'll add that at the very beginning of the interview when the women walks into the shop, in the back, against the wall, you can see a large white and blue container looking thing that says "PDJ Vibro LTD." Looking that up, you find the company's site and learn that is actually metal polishing equipment. This would makes sense to have especially if you're working with metal parts, like the Luke saber.
Rey staff- Off the bat, says "mixture of "PMMA and aluminum," then painted, and hand wraps.
TFA TK/Finn helmet: As they walk toward the Kylo Ren helmet work table, you see all the TFA Trooper helmets on the shelf. On the bottom-left, you can see the black "inserts" of the face. What I notice however is that there appears to be tubular-like "flashing" along to the top of them in the stack. It's hard to tell about the main body of the helmets though. Take that for what you will though. It'd be taken as a sign of either injection-molding or 3D print scaffolding.
Kylo Ren helmet- Bingo, he states:
"a mixture of molded and cast elements like a plastic cast helmet but then we've got 3D printed nose plates. This is a a different type of 3D printed grill (pointing at the chrome of the KR helmet)." He also says "it's a complicated thing to put together because of the different shrinkage rates"
I'm pretty sure coming from the guy's mouth directly kinda has a more definitive answer to these questions. I was really skeptical about the idea of selling direct 3D printed pieces as replicas though. I'll still believe that the melted vader is the only piece that's 100% 3D printed, but the other items, as the guy stated, are a mix of things and he did state the KR helmets are indeed from a mold w/ the add-on of 3d printed pieces.