In optical fiber wire (UV wire), only the UV cure resin is directly coated over the clad.
In a practical optical fiber wire, the coating is double-layer. The first coating over the clad is called as primary coating. The second coating on the primary coating is called as secondary coating. The role of primary, and secondary coating is the moderation of external stress, and resistance to the external stress, respectively. The double coatings of acrylate is called as dual acrylate resin coating (coating type: UV cured, dual acrylate).
For an optical fiber with the clad diameter of 125 µm, provided that it has the primary and secondary coating with 30 µm thickness each, and a 5µm thickness coloring layer coated on the secondary coating for an identification of the fiber splicing point, its coating diameter is 250 µm. This is 0.25 mm optical fiber wire.