A standard Impressions Signs and Printing custom channel letter is a 3-dimensional graphic sign element. Its channel is fabricated from sheet metal, most often aluminum since it will not rust. The sheet of aluminum is cut on our CNC table by a computer-controlled router. This creates the back of the channel and is the basis for the letter shape. Channel Letters are custom made metal or plastic letters that are commonly used on the buildings of businesses and organizations for exterior signage.