Felt Side

The top side of a sheet or web of paper, or the side that has not formed in contact with the papermaking machine's forming wire, as opposed to the wire side. As water drains down through the wire mesh belt from the papermaking furnish, small fibers (called fines), fillers, and sizing are lost through the mesh. Consequently, the felt side contains more fines, fillers, and sizing than the wire side. The paper's grain is also less pronounced on the felt side, and the felt side also has a less "wild" formation. Since the felt side contains more filler, it is somewhat weaker than the wire side, and is often not the preferred side for printing. Paper that is to be folded also has a greater tendency to crack when the felt side is on the outside of a fold. Since it also has more fines, many of which remain as loose particles, printing on the felt side results in greater piling of paper debris on the blanket. However, the felt side of paper is preferred for other printing applications, especially for writing with a pen and ink, as feathering is minimal on the felt side. Letterheads are typically printed felt side up, and envelopes folded felt side out. A watermark will read forward from the felt side.

A paper's two-sidedness is primarily caused by using a traditional single-wire fourdrinier paper machine. The disparity between the two sides can be minimized by using a twin-wire former which sandwiches the papermaking furnish between two wires, imparting to the paper two wire sides. (See also Wire Side.)

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