white tie/black tie

[Guest]

Hello.
What is the best cloth to be used for white-tie and black-tie suits? I know barathea is the common fabric but is that the only fabric that can be used? Is it the only correct and most traditional?
Thanks

[Guest]

The gossip columnist Lord Castlerosse (whose publicly turulent marriage to Doris Lavigne was suposed to be the real life basis for the Noel Coward Play Private Lives), used to wear inky blue vicuna for evening wear and declaim: "What's the good of being a Viscount, if you can't live on credit!" Loro Piana claim to have a monopoly on this cloth.
NJS