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.
In 2007, the United States Postal Service unveiled the Forever stamp, a non-denominated stamp that can be used, as its name implies, forever. Even when the cost of a stamp fluctuates, a forever stamp can still be used to mail a letter that weighs one ounce or less within the U.S. with no additional postage necessary. As an example, in 2013, it cost $0.46 to mail a letter weighing one ounce or less within the United States.