Interleaved 2 of 5 is based on Standard 2 of 5 symbology, but uses both bar and space width to encode information so the density of Interleaved 2 of 5 is much higher.
It is primarily used in the warehouse industry.

Interleaved 2 of 5 encodes any even number of numeric characters in the width of both bars and spaces.

It is called “Interleaved” because 2 characters are encoded in a unit of 5 bars and spaces. The even position character is encoded into bars whilst the odd position character is encoded into spaces. Thus, Interleaved 2 of 5 symbology can only encode data elements with even number length.

Interleaved 2 of 5 is a numeric symbology.
It character set only include 10 digital characters (0, 1, 2, 3, 4, 5, 6, 7, 8, 9).
Similar to Standard 2 of 5, the Interleaved 2 of 5 can include an optional modulo 10 check digit.
Interleaved 2 of 5 is a continuous symbology.

1. Interleaved 2 of 5 Mod 10
2. USS ITF 2/5, I-2/5 or ITF 2of5

A typical Interleaved 2 of 5 barcode has the following structure:
1. A start character 1010
2. Message encoded
3. A stop character 1101

1. Start with the right-most digit in the message; mark the character with even and odd position.
The right-most digit has the even position.
2. Sum all digits in the odd position
3. Sum all digits in the even position, and then multiply by 3
4. Add the result 2 and result 3
5. Divide the result of step 4 by 10, the check digit is the result equal to that 10 minus the remainder

Another variant of Interleaved 2 of 5 is ITF-14 which encodes EAN/UCC-14(also called SCC-14).

Sometimes ITF-14 also includes an add-on symbol with five-digit input followed by a checksum digit.

The add-on symbol is separated from the primary symbol by white spaces.