CindyA,
To begin with, the post office would only let me put my stamp on the outside of the clear envelope. Then, I insisted on putting the envelope on the postcard inside the envelope. Because one of the postcards I sent the stamp fell off and my friend had to pay to get it. Now, if my card is especially puffy, I use a small bubble mailer. (It does cost more to send.) And, I also use the 4 1/2 x 6 3/4" envelopes that I got at Wal-mart. These I only get charged by the weight and it is most times just the price of a stamp. Hope this helps you.