I've mailed things that are pretty solidly needle felted in an envelope...I wrap them in some bubble wrap first. Something lightly felted I mail in a box with bubble wrap and packing peanuts to keep it from bouncing around.
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~Dannielle
Momma to Isabelle (8/95) and Mason (1/01)
I got interupted mid click....story of my life, I pm'd you but didn't realize at the time you were refering to needle stuff.
I don't do a whole lot of needle felted stuff. But if it's rather small and you pack it up snug with bubble or paper, it should fair just fine in a poly mailer.
Most fragile-like things I put in a box. It should still be light enough to fall under first class shipping weights.