> Helium balloon. The balloon was attached to a weight. The address was written on the balloon with magic marker; no postage was affixed. Our operative argued strongly that he should be charged a negative postage and refunded the postal fees, because the transport airplane would actually be lighter as a result of our postal item. This line of reasoning merely received a laugh from the clerk. The balloon was refused; reasons given: transportation of helium, not wrapped.
From a set of year 2000 USPS experiments:
> Helium balloon. The balloon was attached to a weight. The address was written on the balloon with magic marker; no postage was affixed. Our operative argued strongly that he should be charged a negative postage and refunded the postal fees, because the transport airplane would actually be lighter as a result of our postal item. This line of reasoning merely received a laugh from the clerk. The balloon was refused; reasons given: transportation of helium, not wrapped.
https://improbable.com/airchives/paperair/volume6/v6i4/TMP-1...
Image links are dead, including on archive.org :(