Flyers are packed to safely survive the postal system.
The flyers are packaged in a plastic sleeve with the top of the plastic sleeve taped shut to prevent any water damage.
Sheets of cardboard are also packed with the flyer to help strengthen the letter so that it doesn't bend easily.
All flyers are sent in a cardboard envelope.
"Do Not Bend" is also written on the envelope.
Orders of larger quantities will have a piece of MDF in the envelope for an extremely solid letter that is unbendable. Orders of very large quantities are packed inside a cardboard box.