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Can You Send Inflated Mylar Balloons in the Mail?

Sending an inflated Mylar balloon through the U.S. Mail in an approved box is legal in most cases--but may not be the most reliable way to send your good wishes across the country.

Air-filled Mylar
- Use an appropriate box to ship the balloon.
  
  Mylar is a type of polyester with an aluminum coating of microscopic thickness. Air-filled Mylar is not restricted by the U.S. Postal Service.
Helium
- Helium-filled Mylar balloon
  
  Under U.S. Postal Service regulations, helium is a non-flammable, non-toxic gas classified as "Division 2.2." These materials may be sent through domestic U.S. mail (both surface mail and air mail), but not through international mail, according to the "U.S. Domestic Mail Manual."
Air Mail
- At high altitudes, air pressure is extremely low.
  
  Sending an inflated balloon via domestic air mail, though legal, may cause it to pop in the unpressurized cargo hold.
Local Air Pressure Differences
- As altitude increases, air pressure decreases.
  
  Sending an inflated balloon to a significantly higher altitude (e.g. from sea level to the Rocky Mountain region) may cause it to pop. Sending it to a lower altitude (e.g. from the Rocky Mountain region to sea level) may cause it to partially deflate.

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