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.
Re: Using stamps - getting the amount correct with new stamps? The Forever stamp is always going to be worth whatever the current postage rate for 1 ounce is. So even you bought it for 46 cents it is now worth 49 cents of postage. I always have a small supply of add on stamps that I can attach for oversize, overweight, second ounce, etc. letters.