I presume it's aluminized mylar, or would be if it's ever made. That way it would be both helium"proof" and radar-reflective. I find enough balloon shreds in the mountains to know they can last a long while and travel great distances.

I've seen rolled plastic rescue streamers that can trail behind a lifeboat or across a snowfield or meadow, but they presuppose a large empty expanse to use.

Cheers,

Rick
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--Rick