Don't get me started on Mylar balloons. I work offshore, and you guys have no idea how many I see every day off the coast of California. I believe they mostly come from cruise ships. I'm not really a tree hugger, but in my opinion, the balloons on cruise ships should be made of biodegradable materials.
Mylar lasts decades in the water....
I've also launched latex weather balloons (6' diameter) from my boat for the navy weather guys. Those go up 80,000 ft they say before popping. They sometimes have 6" aluminum spheres dangling below them, over 100' on "kite string".
When I asked about the impact to a jet engine, they said that because the string was 42# breaking strength, it was legal. Of course I then asked what the breaking strength and impact of the metal sphere would be to a jet engine...
I'm considered somewhat of a trouble maker at work. I'm not sure why though. :-p