Selection of wire insulation has a direct effect on product performance, cost, and manufacturability during the design and manufacture of electronic components such as high-frequency transformers, network filters and power supplies. At present, the most popular types of insulated wires are Triple Insulated Wire (TIW) and Fully Insulated Wire (FIW). Both satisfy reinforced insulation requirement, however, there are huge differences in the structure, process and application scenarios.

TIW (Triple Insulated Wire) is formed by three separate layers of insulation material are extruded over the conductor. It has a high mechanical strength and high insulation security and has been a popular choice for switching power supply transformers for a long time.

FIW (Fully Insulated Wire) is a new kind of fully insulated wire. Its insulation layer is composed of an integrated or multi-layer fusion structure, which is more homogeneous and thinner, and it also has good solderability.

The most significant difference between the two lies in the soldering method:

TIW wire requires stripping or the use of special flux before soldering. Otherwise, the insulation layer cannot be removed, leading to cold solder joints or poor electrical connections. This adds steps such as wire stripping or adding insulating sleeves, and imposes higher requirements on automated equipment.

FIW wire supports direct soldering. When immersed in high-temperature solder (around 390°C), its insulation layer automatically melts, shrinks, and peels off, exposing a clean conductor surface without any pre-treatment. This feature greatly simplifies the production process and reduces labor and equipment costs.

Fully insulated wire has a thinner and more uniform enamel coating. For the same conductor cross-sectional area, the overall outer diameter of FIW is typically smaller than that of TIW, which facilitates miniaturization and high-density design of transformers and inductors. Additionally, since no extra sleeves or barriers are needed, the winding window utilization rate is higher.

Both types meet the requirements for reinforced insulation, with conventional voltage withstand ratings above 3000V, and some FIW wire specifications reaching 5000–8000V. However, in practical selection: Tripe insulated wire is more suitable for traditional, well-established applications and larger transformers that require higher mechanical strength of the insulation layer. FIW wire is better suited for scenarios that demand high efficiency, miniaturization, and automated production, such as phone chargers, smart meters, network transformers, and automotive electronics.

In short, TIW wire requires stripping, while FIW wire can be soldered directly. If your production line pursues efficiency, process simplification, and cost reduction, FIW is a new option worth prioritizing. If your product has special requirements for the mechanical structure of the insulation layer or relies on a mature existing solution, TIW remains a reliable choice.

As electronic components move toward miniaturization, higher frequencies, and greater reliability, the application of FIW is rapidly expanding, becoming an important technological direction to replace traditional TIW.