I bought a pack of SDK recently and noticed the plastic feels just like the simple ultra. This was a batch when the incorrect “light blue” backing was applied making it look darker.
See this thread: https://www.adisc.org/forum/threads/changes-to-abu-sdks.139849/
I actually really like the Ultra plastic so apart from the horrid blue it feels much better than the old style and it fits better too (single taped nappies don’t usually fit well on me).
However I do remember reading somewhere (I am not sure where, here or reddit?) that ABU were reverting on some plastic changes and going back to the original. Does anyone know if this is what they were talking about? I hope not because these fit and feel much better - just without that horrid blue.