If you have a poster that you want to preserve and make it appear more like piece of art hanging in a gallery, you can make a mat for it. If you are making your own posters to sell, then you will definitely need to mat it to make it look more professional and shrink-wrap it to protect it during the shipping process. As long as you have the right equipment and follow the right steps, you can do this yourself at home.
Buy two 2-ply pieces of mat board that are slightly larger (at least 3 inches all the way around) than the poster you want to mat. If the pieces of mat board are too big, add 6 inches to the height and width of the poster, and measure and cut the mat boards to this size. Use a matting T or a tape measure to measure from the edges of the boards and trace a straight line lightly with a pencil. Cut along the lines with a matting knife or a utility knife.
Measure and cut out the framing window of the front piece of the mat. If you want the inside edges of the frame window to overlap the edges of the poster by 1 inch, measure from the outside of the mat board to the center 4 inches (if you made the mounting board 3 inches larger than the poster on all sides). Mark the measurement with light pencil lines. Cut along the lines with your matting knife.
Position the poster on the back piece of the mat and measure to make sure you have 3 inches of space on all sides. Hold the poster in place with photograph corners. Lay the front piece above the back piece so that the top edges are touching and the side that you want as the inside of the frame is facing up. Place masking tape along the top edges so that the two pieces are attached and the tape acts as a hinge. Bring the front piece down on top of the poster.
Unroll a piece of shrink wrap that is twice as wide as the matted poster and three times as long. Place the poster on the shrink wrap. Fold the end of the shrink wrap over the top of the poster so that it is covered on both sides and the shrink wrap extends from all sides of the matted poster, at about half the width of the matted poster.
Fold the open edges of the shrink wrap over slightly as you move a heat gun along them to seal them shut. Hold the folded edges down with any long instrument to prevent burning your fingers. Apply heat evenly over the whole surface of the plastic until it lies tightly against the matted poster.