Almost all Kilts worn today are a modern expression of older forms of dress common in the "highlands" which at one time extended in a crescent from Donegal across the top of Ulster to the Mull of Kintyre and the Highlands and Islands of Scotland.
The "Big Kilt" was a type of cloth armour, the pleats of which were very resistant to sword cuts and the piercing of spears.
As this garb included the tradition of soaking the shirt in goose grease to make it waterproof, fully "traditional" garments are best left to historical societies! The modern "small" kilt looks traditional and reflects older traditions while being practical and more fitting for polite society than the battlefield or cattle raid.
Historians tell us that the "kilt" is a misreading of old engravings. It is probable that originally the outfit was an all-in-one long belted shirt rather than two separate garments. You could look at What the Irish wore to see examples of these garments.
Some argue that the modern kilt is a dreadful historical error. Click here
All we will venture to say is that the modern Irish Kilt is as "traditional" as any other modern kilt - no more and no less.
"National" dress is a dress not in common use but chosen to reflect a nation's image of itself. In 1947 India chose not to adopt the loin cloth of Gandhi but wanting to have a formal national garb invented the collar-less "Nehru" suit.
In 1900 Padraig Pearse (who in 1916 read the declaration of Irish Independence and was shot a few days later) was asked to suggest a "National" dress. In his reply he said "Frankly, I would much prefer to see you arrayed in a kilt . . . (rather than traditional types of Irish trousers)"
The illustration shows Pearse's school St Enda's with the boys in kilts. The man overseeing the drill, Con Colbert, was one of those executed in 1916 with Willy Pearse another leading kilt wearer. None of the pupils attending the school in 1916 took part in the Rising. While some former pupils did fight (they would have been young men by the time of the Rebellion), none were killed, though many were sent to prison as a result of their involvement.
Kilts had been worn since the mid 1800's by Celtic revivalists of all sorts and as a result the kilt was a natural choice.
Although the first President of Ireland wore the Saffron kilt,the kilt as a form of dress today it is mainly worn inside Ireland for dance wear and by pipe bands.