The original signature plastics PBT SA sets were “Industrial” and “Ice Caps” These were dye sublimated PBT. However, SP adapted their all R3 ABS doubleshot molds to produce the caps. Not sure how that works, but they were never quite happy with the result. I own both sets. You can tell when you have them on a board that they have a lot of shrinkage going on. You can actually see extra space between the caps.
SP made all new molds for SA profile (fully sculpted) PBT keycaps and tested it for a long time. I seem to remember them talking about the process at least 2 years ago. Their SA-P “industrial” set was the first run of these new molds. The texture is different, the profile is now fully sculpted, and I believe the caps are actually slightly thicker.
Anywhoo… you can now get very nice SA profile (fully sculpted) in PBT with beautiful dye sublimation. And the new “Snow Caps” are the remake of the “Ice Caps” but with the new SA-P molds.