I2 of 5(Interleaved 2 of 5) is often thought of as a numeric-only counterpart to Code 39. Whereas Code 39 has become the standard in alpha-numeric coding, I2 of 5 enjoys a similar status in the industries that use numeric-only information. Like Code 39, I2 of 5 is also recommended for use on corrugated shipping containers.

        I2 of 5 is a high-density, bi-directional code that encodes characters as well as spaces. Each character is made up of five bars OR five spaces (not both). Each character has two elements that are wide and three elements that are narrow. Since this code is a variable-length code, it must be printed with a frame around the code to ensure an accurate read. The frame serves as a block to guard against a short diagonal read. Shown in Figure 1 is the Interleaved 2 of 5 bar code for the number 1021.

        The I2 of 5 code derives its name from the fact that each character is made up of five spaces or bars and that two characters are interleaved together. In this code, the odd-positioned numbers are first, third, fifth, etc., whereas the even-positioned numbers are second, fourth, sixth, etc. Positions of the code are represented by the spaces as shown on Figure 2. For instance, the number 19 has its 1 represented by the bars and its 9 represented by the spaces. Since the characters are all coded as pairs, any number with an odd number of digits must be padded with a zero. For instance, the number 710 is encoded as 0710 so that all characters (in this case the 7) can be paired and interleaved with others.