The first polyester fibers were produced by reacting ethylene glycol and either terephthalic acid or one of its esters to give poly(ethylene terephthalate). This polymer is still used to make thin films (Mylar) and textile fibers (Dacron and Fortrel).
This stamp also may be used for mailing items weighing up to 2-ounces. These Forever stamps will always be equal in value to the applicable price for the price category printed on them, at the time of use. The initial price and value for this stamp is 71 cents, effective May 31.
4.) British Guiana 1-cent Magenta Stamp (1856). Alleged to be the world's rarest and most valuable stamps, these stamps were sold at an auction in 1970 for $280,000. At present, this rare stamp value is estimated over a million dollars. There is only one specimen left for this most expensive ever.