Abstract: A multiple turn coil adapted to be inserted in a slot of a rotor in a dynamoelectric machine is formed by a bundle of individually insulated parallel bars of electroconductive material arranged close together and surrounded, in the vicinity of each slot section of the coil, by a pre-formed tube of substantially non-compressible, non-thermoplastic dielectric material (e.g., polyimide film), the wall of which is thin and flexible enough to bend in any plane and smooth enough to permit substantially unfettered longitudinal expansion and contraction of the insulated conductors inside the tube. Inside the coil a cross-shaped member of the same dielectric material enhances the turn-to-turn insulation.