Each post card is quilted on the front, contains a stiff middle "batting", and a piece of card stock on the back stamped to look like a postcard so you can write a note.  And, yes, they can be sent through the mail. I usually take mine to the post office just to make sure I've got the right postage - usually around $.70.  Cards are 4" x 6". Each card comes with a plastic sleeve that can be used as an envelope.