The migration of impurities due to non-cellulosic material, acidic material from ground wood papers, acid from writing ink, and other materials is considered. The author recommends that material to be stored in contact with documents of value should contain no ground wood fibers, have an acidity on the pH scale of not less than pH 5.0, and after an aging test of 72 hours at 100 degrees Centigrade should not lose more than 25% folding endurance. He also cautions that contact with newspaper clippings, photostats, cellulose nitrate film, paper clips, pins, rubber bands, and other materials may prove dangerous to valuable documents.