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.
You can use first class Forever Stamps for international mail, but since international prices are higher than domestic prices, you have to add additional postage. The value of the Forever Stamp is the domestic First-Class Mail letter price. So here are your options: First Class International Forever Stamp: $1.15 (as of Dec 2017). That covers 1 ounce. For every additional ounce you need to add $0.21 worth of postage. or. Standard domestic Forever Stamps which are worth $0.49 (as of Dec 2017). You will need at least 3 to cover the international cost of the first ounce which is $1.15.