Thanks to citizens everywhere, the world now recycles just over 50 percent of the paper it uses, according to various estimates. Reprocessing plants are sprouting widely. But trees will never be fully spared because of a quirk of wood fibers themselves.

Virgin pulp is rich in water, which provides for ample hydrogen bonding that holds fibers together when made into paper. But each time a fiber is cleaned, de-inked and dried in a reprocessing plant, "only 80 percent of the bonds recover," explains Yulin Deng, associate -professor of chemical and biomolecular engineering at the Georgia Institute of Technology. After four or five recyclings, he says, "a fiber can no longer make strong enough bonds" and becomes waste.

This article was originally published with the title Gunk-Free Fiber.

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