For my last mail piece, I tried something that I wasn’t sure would get sent through at all! After checking the mail regulations, I couldn’t quite tell if something like this would go through the mail without an envelope:
It’s a ball of model magic, which was soft at the time and very easily deformed. So for anybody to be able to read the address as it goes through the mail, it will have to be kept in about the same shape as it was originally sent.
When I took this to the post office, the man at the counter didn’t think it would get sent. I insisted that it didn’t break any regulations, so he asked for a second opinion from someone nearby, who said “Sure, why not? It’s not liquid, fragile, or perishable. But he needs a return address.” So I wrote my return address on the ball and it was accepted!