Unobtainium - An engineer friend of mine used that term a decade + before that movie came out, “It’s expensive, it’s in submarine hulls and expensive motorcycle parts” was his joke.
He has a Saharan wit, seeing an A-arm assembly on the side of the road on the way to a job one day elicited the comment “You NEED those”...
I believe that unobtanium was used to build the boring vessel in the movie, The Core.