The pocket square — folds, colours and context
The white pocket square — in linen or fine cotton — is the most formally correct and the most versatile. It works with any suit, any tie colour, any occasion. The flat fold — where the square is folded to show a clean white rectangle — is the most formal. The one-point fold shows a single triangle of white. The puff fold creates a loose, relaxed mound of cloth in the pocket — less formal, more personal.
A coloured or patterned pocket square adds personality and should relate to the colours of the outfit — not match them exactly (a tie and pocket square in identical pattern look costume-like) but echo them: a pocket square that picks up one of the secondary colours in the tie pattern, or complements the jacket cloth, reads as considered and deliberate.
In silk, a pocket square has a slight sheen and a soft hand that drapes easily. In linen, it is crisper and more structured. In cotton lawn, it is intermediate. Each suits a slightly different occasion and a slightly different suit.