Happy Birthday Mylar Birthday Balloon
The design is the same on both sides of the balloon.
Size: 18" across. It's uninflated, so you can either blow it up with air or have it filled with helium at your neighborhood party store or florist.
To inflate with air, gently insert a plastic drinking straw through the round hole in the neck of the balloon so it extends into the main body of the balloon, and blow into the straw to inflate. When fully inflated, pull out the straw and the balloon's neck will automatically seal. To deflate for future re-use, gently reinsert the straw as before (to its full length) and allow the balloon to deflate.