Polyester Film
Electrical insulation and layer separation in cable construction
Polyester Film
Polyester film (PET) is a thermoplastic film that combines dimensional stability, mechanical strength and consistent dielectric properties across a wide thickness range. Its molecular structure makes it the reference material for electrical insulation in cable manufacturing, with a surface resistivity of 1.5×10¹³ Ω and volume resistivity of 2.0×10¹⁴ Ω·m per ASTM D257.
In cable construction, polyester film acts as a separator between conductive layers, as primary insulation or as reinforcement of the main insulation. Its smooth surface eases high-speed helical taping and its tensile strength (170–190 N/mm² depending on thickness) ensures integrity through the manufacturing process, without breaks or deformation.
Thicknesses range from 12 to 350 µm, with dielectric strength from 3.4 kV at the finest thickness up to 16.9 kV at 125 µm. This range allows the insulation level to be matched to each construction's requirements, from instrumentation cables to power cables.
In cable applications, polyester film is not selected for its dielectric strength alone. Behaviour during taping, dimensional stability under tension and thickness repeatability are critical factors for a stable construction in continuous production.
During high-speed helical taping, the combination of tensile strength and controlled PET elongation prevents breaks, drag-out and pitch variations, supporting stable manufacturing even in multilayer constructions.
How to choose the right one?
The right thickness depends on the balance between required insulation level, available space in the construction and mechanical demands during manufacturing. The most common thicknesses and their typical use by cable type are summarised below.
| Thickness | Dielectric strength | Typical application | When to choose |
|---|---|---|---|
| 12 µm | 3.4 kV | Fine separation between conductors | Tight spaces, optimised cost |
| 19 µm | 5.1 kV | Standard insulation in instrumentation cables | Cost/performance balance |
| 23 µm | 7.9 kV | Separation in pair and data cables | General use, good handling |
| 36 µm | 9.0 kV | Reinforced insulation | Higher dielectric strength required |
| 50 µm | 10.8 kV | Low-voltage power cables | High mechanical strength |
| 75 µm | 13.3 kV | Primary insulation in special cables | High elongation (min. 120%) |
| 125 µm | 16.9 kV | Maximum insulation | Demanding processes, maximum protection |
Additional thicknesses available on request: 15, 150, 190, 250 and 350 µm.
Technical specifications
The mechanical and electrical values shown below come from tests run to international standards and characterise the material's behaviour both during processing and in service.
| Property | Method | 12 µm | 19 µm | 23 µm | 36 µm | 50 µm | 75 µm | 125 µm |
|---|---|---|---|---|---|---|---|---|
| Grammage (g/m²) | — | 17 | 26.6 | 32.2 | 50.4 | 70.0 | 105.0 | 175.0 |
| Tensile strength (N/mm², min.) | ASTM D882 | 170 | 190 | 190 | 190 | 190 | 180 | 170 |
| Elongation at break (%, min.) | ASTM D882 | 90 | 90 | 90 | 90 | 90 | 120 | 120 |
| Dielectric strength (kV) | JIS C2151 | 3.4 | 5.1 | 7.9 | 9.0 | 10.8 | 13.3 | 16.9 |
| Thermal shrinkage (%, 150°C/30 min) | — | 2.8 | 2.8 | 2.8 | 2.8 | 2.8 | 3.0 | 2.8 |
Electrical properties (common to all thicknesses)
| Property | Value | Test method |
|---|---|---|
| Surface resistivity | 1.5×10¹³ Ω | ASTM D257 |
| Volume resistivity | 2.0×10¹⁴ Ω·m | ASTM D257 |
Values shown are typical and do not constitute binding specifications.
Available variants
Colours and finishes
- Natural (transparent) — standard
- Black (opaque)
- Milky white
- Increased opacity (hazy)
- Custom colours on request
Special treatments
- Application-specific surface treatments available on request.
Alternative materials
- Polyethylene film (PE)
- Compact polypropylene film (PP)
Delivery formats
The supply format directly influences process continuity and taping efficiency. Material can be supplied in different formats and dimensions adapted to each machine type and production speed.
Pad / Roll (pancake)
Flat reel for conventional taping
Spool (TWS / STS reel)
Reel for feeding taping machines
Other formats and dimensions available on request. Custom slitting service available.
Application sectors
Need technical advice?
Our technical team is available to help you select the optimum material for your application.
Custom slitting
Up to 1200 mm width, ±0.50 mm tolerance
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Spooling
Pad to TWS/STS spool conversion
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Need technical advice?
Our technical team is available to help you select the optimal material for your application.
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