IEC 60794-1-308: 2023 describes test procedures to evaluates the degree of permanent twist in an uncabled ribbon or in a cabled optical fibre ribbon. This document applies to optical fibre ribbons in optical cables for use with telecommunication equipment and devices employing similar techniques, and to optical fibre ribbons in cables having a combination of both optical fibres and electrical conductors. This document is not applicable to partially-bonded ribbons. The method for partially-bonded ribbons is under consideration. Throughout the document, the wording "optical cable" can also include optical fibre units, microduct fibre units, etc. NOTE The environmental testing of optical fibre ribbon would be valuable for some applications. Useful information about suitable test methods can be found in the optical fibre standards IEC 60793-1-50, IEC 60793‑1‑51, IEC 60793‑1‑52, and IEC 60793-1-53.