Interleaved 2 of 5
Interleaving is the mechanism from which Interleaved 2 of 5 takes its name: one digit is encoded in five bars and the next in the five intervening spaces, so a pair of digits occupies the width a single digit would otherwise need. Intermec published the design in 1972. The doubled density carries a structural constraint, since payloads must contain an even number of digits and an odd-length number is padded with a leading zero. The character set is numeric only, the X-dimension is typically 0.19 mm, and ten-module quiet zones are required. Without bearer bars, partial scans are a documented hazard, which is why the GS1 case-level variant ITF-14 adds them. Generic Interleaved 2 of 5 is not a GS1 data carrier.
A high-density numeric-only symbology that encodes pairs of digits by interleaving one digit in the bars and the next in the spaces. This dual-encoding approach doubles density compared to non-interleaved formats, but requires an even number of digits.