Highly compressible open reinforcing cord

A cord comprising a single layer made up of N helically wound metal filamentary elements having an outer diameter D, each metal filamentary element describing, when the cord extends in a substantially rectilinear direction, a helical path about a main axis substantially parallel to the substantially rectilinear direction, such that, in a section plane substantially perpendicular to the main axis, a distance between a center of each metal filamentary element and the main axis is equal to half a helix diameter Dh and is substantially constant and identical for all the metal filamentary elements, the metal filamentary elements defining an internal enclosure of a cord of diameter Dv, each metal filamentary element having a diameter Df and a helix radius of curvature Rf defined by Rf=P/(π×Sin(2α)), where P is a pitch of each metal filamentary element expressed in millimeters and α is a helix angle of each metal filamentary element,

• wherein, with Dh, D, Dv, Df and Rf being expressed in millimeters:
• 0.10≤Jr≤0.25
• 9≤Rf/Df≤30, and
• 1.60≤Dv/Df≤3.20,
• where Jr=N/(π*(D−Df))×(Dh×Sin(π/N)−(Df/Cos(α×π/180))), α is the helix angle, expressed in degrees, of each metal filamentary element and Dv=Dh−Df.