A pocket square costs very little and changes a great deal. A white linen square in the breast pocket of a dark jacket, folded flat or puffed softly, finishes the outfit off, which nothing else quite does. Put a colour or a pattern in there instead and you have added personality without saying a word. It takes ten seconds to do well and the difference is visible from the other side of a room. We keep squares in white linen, white cotton and patterned silk here, so you can try them against the jacket rather than guessing.
Folds, colours and knowing when to stop
The white square in linen or fine cotton is the most correct and the most useful. It goes with any suit, any tie and any occasion, and if you own one square this is the one. The flat fold, showing a clean white rectangle above the pocket, is the dressiest. The one-point fold gives you a single triangle. The puff, where the cloth is gathered loosely into the pocket, is easier and more personal, and it is what most of us actually do on a weekday morning.
Colour and pattern should talk to the rest of the outfit without repeating it. Do not buy a tie and a square in the same pattern, because the two together look like a set bought in a hurry, and everybody can tell. Pick up one of the secondary colours in the tie instead, or something that sits well against the jacket cloth. That reads as deliberate, which is the whole idea.
Silk has a little sheen and a soft handle, so it drapes and puffs easily. Linen is crisper and holds a fold sharply, which is why it is the one for a flat point. Cotton lawn sits somewhere between the two. Each suits a slightly different jacket and a slightly different evening, and it is worth owning more than one.