These 4 millimeter holders are the finest quality made today from Dupont's Mylar DŽ or equivalent film. These are the holders we use and are also used by the leading paper money dealers and auction firms. This product is now used by the Library of Congress and the Smithsonian Institue. Mylar DŽ is the purest material presently used for currency storage and will keep your notes for decades. When ordering holders, please provide us with a street address so your order may be shipped via UPS. All Mylar DŽ bank note holders and sheet holders are sent postpaid!