This is simple theft for this bubble-mailer, as the USPS provides it to be used in actual mailing via the USPS.
That said, during the pandemic, my quartermaster went to Costco and stocked up on toilet paper, paper towels, Kleenex, coffee filters, everything we used that was paper. (Famously and semi-comically, he also bought a large 36-roll pack of Charmin for every employee to take home as a “tiny bonus”, which I approved enthusiastically, so his next review included a little extra for being prescient .)
He also placed larger orders for the cardboard cartons we used, and at the time, we loved USPS “Regional Rate” boxes, as the postage was cheaper than anything for everyone east of the Mississippi.
Then the USPS got rid of regional rate, and we found the remaining USPS rate classes to be more expensive than UPS. But what to do with all those now obsolete USPS regional rate cartons? The post office guidance was to recycle them, but that was a horrible waste. So, we used, and continue to use them as cartons for UPS, who does not care about anything beyond their label. The boxes are new and sufficiently strong to survive UPS’s attempts to crush and smash everything, as while they provide night-shift employment for the Incredible Hulk, they should have him lifting trucks with flat tires, not handling the small parcels.
What we do is NOT a crime, or even unethical, as the USPS refuses to let us use the boxes for anything mailed via USPS, and while they try to claim that the boxes remain their property, legal tells us that anything that anyone sends you for free, without prepayment or an invoice, is yours to keep unconditionally, a law that protects little old ladies from being legally obligated to pay for trinkets sent to them unsolicited by unscrupulous mail-order companies, who rely on their customer base to be forgetful.
We tried to use the regional rate boxes when the “Ground Advantage” first appeared, but the geniuses at USPS decided that this was “misuse”, and re-priced the shipment as “priority mail”, the highest rate they could charge for their usual “well get it there in a week or two” service. They were shrill about NOT using that large supply of boxes for ANY USPS shipments, so to hell with them - we will use them, and THEN they can be recycled after they are used at least once for shipping. We have a planet to try and not destroy, and paper-making is not easy on the whole CO2 thing.
So, call me a criminal, a pirate, whatever, but the ethics of the situation are the primary concern here, and if the USPS wants to get their knickers in a wad over this, they cannot impose “terms of use” on an item they sent us for free, and we will happily make a test case of that for them in federal court, as our attorney takes on crusades from time to time, and this is as much a crusade issue as the ever-shifting cesspool of “securities” law, where both the FTC and the DOJ refuse to state anything clearly, and the only way to know “the law” is to read up on who they accused of what, as nearly everyone gets a plea deal, so almost NONE of their ever-expanding “regulations” have actually been contested in a trial with a judge and jury.