Yeah, the SFS 1:1 scale helmets were made by CNC-ing a block of foam making a master, and moulding it, using the 3D-scan of the SFS helmet. They lost some details in the process but later on a miniature (1:3 scale) SFS helmet was 3D-printed which kept the original details captured in the scan and that master was later moulded and minitures were made in 2 runs on the RPF. I actually have one of those from the 2nd run. I think RS is now in possession of the miniture mould.
I think TE also made some vac formed SFS helmets in HDPE. How he produced the vac moulds from 1-piece cast however is beyond my knowledge of mould making. Maybe Chris knows how that could be done?