It is remarkable to me how many people come to SF to ask about pocket squares. The following is a good basic summery by Alan Flusser from his book Clothes and the Man. A simple white handkerchief is all that is necessary to complete the business ensemble. It is also the least expensive way a man can quickly elevate his level of style. The handkerchief, like the hose, gives a man one more opportunity to do something a little out of the ordinary, something a bit more inventive. A white handkerchief placed in the breast pocket of a dark suit offers a touch of elegance and is sure sign of a confident and knowledgeable dresser. The finest white handkerchiefs are made of linen with hand- rolled edges. While they are difficult to find today, they are worth searching for. The virtue of linen is that because of its inherent stiffness, it retains its starched quality throughout the day. It is the only handkerchief fabric that looks as fresh in the evening as it did in the morning, when it was first folded. While a white linen handkerchief is the easiest choice for many, since it is always proper, for those more adventuresome dressers, there are handkerchiefs in colors and patterns. In this case, it is generally the tie that is the determining factor in choosing the proper pocket square. The pocket square must complement the tie, though it should never directly match it in pattern or color. Another possibility is silk. These come in a wide array of solid colors. But instead of solids, wear silk in the traditional English ancient madder patterns, such as paisley or foulard. The colors in these are muted and give a more subtle effect. If your tie is of silk, a handkerchief of a dry linen fabric looks best, while if your tie is of wool or cotton, silk in the breast pocket will add the proper textural balance to the chest area. I like how the white square compliments the silver (or grey) colors in his tie. Subtle yet elegant.