Through engineering of the paper substrate, this characteristic feel can withstand folding, crumpling, soiling, and even laundering.

The substrate also has a distinctive look. The paper used for U.S. banknotes is a blend of two cellulosic plant fibers, flax (also known as linen) and cotton. It is supplied to the Bureau of Engraving and Printing (BEP) by a single manufacturer, Crane and Company in Dalton, Massachusetts. Processing of the substrate, which is tightly controlled, includes the use of selected plant fibers and additives and the development and use of specialized methods for pulping, washing, refining, screening, pressing, and bleaching.

The sources of raw materials are selected by optimizing quality and cost. Both the flax and cotton materials are primarily sourced from waste products from the textile industry. This approach is cost-effective because papermaking can utilize the shorter fibers that make poor thread for cloth. Currently, U.S. currency is made from nominally 25 percent flax and 75 percent cotton fibers. An assortment of papermaking chemicals—color, strength, and sizing agents—are added to the raw materials. No starch or clay agents are employed in currency paper, although these are added to most other high-quality papers to improve brightness. This difference contributes to the unique look of currency paper.1 See Box B-1 for further details on papermaking, which convey the difficulties inherent in duplicating the “feel” of genuine currency paper.

Added Elements

A number of additional items are added to the substrate during the papermaking process. These include short fibers that are visually apparent as short red and blue threads in the paper itself. A watermark is made during the papermaking process in the $5, $10, $20, $50, and $100 notes. The watermark depicts the same historical figure as that shown on the respective bills’ engraved portraits.

Higher-denomination notes also incorporate security strips, made of thin plastic embedded in the notes in the final stages of papermaking; these are marked by metallic print indicating the denomination of each note. In newer notes, the strip also contains a tiny graphic of American flags.2 The strips have a unique position on each denomination as well as a unique fluorescent color under ultraviolet

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