Insulated sleeving and covered wires are to-day so fundamental and so common a part of electronic service equipment that their use has tended to become somewhat of a habit, and at times insufficient importance is attached to their selection.This paper, which is restricted to the field of internal set-wiring, attempts to stress the importance of careful consideration in the choice of the wire covering, and also draws attention to the need for standardization and rationalization of the types and sizes of wire coverings employed.A brief résumé is given of the functions which the wire covering has to fulfil; the materials available to meet these requirements are considered, their limitations indicated and the manufacturing processes reviewed.Whatever method or material is used, the final product is judged on its ability to pass the inter-Service specifications now mandatory; these specifications are fully discussed, the test equipment involved described and test results quoted.It will be seen that there are certain requirements not fully met by the wire coverings available, for which the set designer must make adequate allowance, and the paper concludes with an indication of the likely trend of Service requirements together with suggestions for materials and methods by which these requirements may be fulfilled.