These blank index cards are made of the highest quality 14pt paper. These postcards are great for taking notes, making flash cards, making your own mail-able postcard, and many more methods. These postcards have one side that has USPS approved mailing lines and a stamp box allowing for easy mailing. The reverse side is blank. Each pack comes with a bundle of 50 postcards. These cards are uncoated which means you can use the following to write on with no problems: Pens (gel, ball point, etc.), pencils, permanent markers, highlighters, ink stamps, markers, colored pencils, and many more. There are so many possibilities that they all can't be listed. These postcards are made in the USA and may be used in printers (depending on printer settings - may not fit in all printers).