Mailing a matted 13 x 19 poster? No problem.

Finding an easy way to mail a flat, matted poster is a bit of a problem since there are no standard size envelopes that will hold up in the mail. Here's a simple and elegant solution, and the only cost is for packaging tape and postage.

Here's what you need:
1. Two (2) Priority or Express Mail boxes (15.5" x 21.5")  from your local US post office. These are free.
2. Packaging tape
3. Box cutter
4. Pencil

Step 1: Step One: The interior protective envelope

First, we need to make an interior envelope for the poster to add an extra later of protection and make the whole package harder to damage or bend. We'll take one of the flat boxes and create a tongue flap closure to make a snug envelope.

Start by turning the box so that the short side is towards you.

1. In the lower left of one of the boxes, measure and pencil out a 13.5 x 19.5 inch box.

2. Cut along the 13.5" side, removing and discarding the entire 15.5" x 2" portion.

3. On the 19.5" side, mark out a 7.5" x 2" rectangle in the top right, and another in the bottom right.

4. Cut out those 7.5" x 2" rectangles, leaving a 4.5" x 2" tongue in the center.

Comments

[electfire]

I would also add some rigid plastic, to help strengthen the cardboard,
along the axes. (I mean plural of axis not of ax{e?}!
^{I hate the English language at times!}

Anyways that would help against bending, though lightweight rigid plastic might be hard to come by, unless you collect "random" stuff
(like my workspace does!)

On a side note, I wasn't aware that the USPS actually give those boxes for free. Thanks for the info!
^{(Wonder if they would mind me taking a bunch, for "projects")}