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.
General rules that are usually, but not always, true for stamp collecting values. â¢ Mint stamps with original gum on the back are worth more than used stamps. â¢Earlier stamps are worth more than modern stamps. â¢Stamps with any faults (creases, tears, thins, etc.) are worth far less than those in perfect condition.