How to choose between PEEK and PI cables? A comparison across six dimensions

These two materials are often priced together as synonyms for “high-end high-temperature resistant”, but they each have their strengths and weaknesses in six dimensions, and the distribution of these strengths and weaknesses is very uneven – in some dimensions, the difference is an order of magnitude, while in other dimensions, the difference is only a little bit, but it determines the success or failure.

 

To state the conclusion first

For resistance to media, abrasion resistance, high-volume extrusion capability, and controllable batch costs—choose PEEK. For extremely thin walls, maximizing weight reduction, cryogenic or high-vacuum operation, and strong radiation resistance—choose PI. If you want both, the correct answer is usually not an either-or choice, but a hybrid structure of PI insulation and a PEEK sheath.

 

1. Temperature resistance: They may seem similar, but the actual difference lies in “how long they can withstand the temperature”.

PEEK operates at 250°C continuously, and above 300°C for short periods; PI operates at 260–300°C continuously, and up to 400°C for short periods. Looking at the numbers alone, the difference is not significant.

However, these figures cannot be directly compared because their thermal failure mechanisms are completely different:

PEEK is a thermoplastic material that softens and deforms before reaching its melting point, with failure manifested as a gradual decline in mechanical properties. It is considered “usable for a long time” at 250°C, but its creep resistance significantly decreases once temperatures exceed 300°C and mechanical stress is applied.

PI is a thermosetting/aromatic heterocyclic structure with no melting point; its failure manifests as thermal oxidative decomposition. It does not soften at 400°C but rather slowly carbonizes—therefore, in short-term high-temperature impact scenarios (such as reentry, engine nacelle, and fire zone crossing), PI has a larger margin than the numbers indicate.

Selection Tips: If your operating conditions are “long-term steady-state at 250℃”, both can handle the task, and it is more cost-effective than PEEK. If it is “normally 200℃, with occasional shocks above 350℃”, the short-term margin of PI is worth paying a premium for.

 

1. Weight: This is the easiest item to get wrong.

Many people intuitively believe that PI is lighter because “PI is a high-end material.” Others have checked density tables and found that PI has a density of about 1.42 g/cm³, while PEEK has a density of about 1.30 g/cm³, thus concluding that “PEEK is lighter.”

Neither conclusion is entirely accurate. While PI does have a higher density, its advantage lies in its wall thickness: PI insulation is formed by wrapping thin films, with single layers as thin as 0.025 mm; whereas PEEK, as an extruded material, is limited by processing and concentricity, resulting in a much higher minimum wall thickness. Under the same electrical strength requirements, PI insulation can achieve a fraction of the thickness of PEEK insulation.

Therefore, the correct comparison method is to compare the weight per unit length (g/m) of the entire cable, rather than the material density. Empirically, PI (Polymer Inductance) significantly reduces weight for small-section signal cables; for large-section power cables, where conductor weight is dominant, the weight difference between the two is diluted, making the cost premium of PI less worthwhile.

 

III. Chemical resistance: PEEK is significantly superior.

This is one of the dimensions where the two differ the most.

medium	PEEK	PI
Aviation hydraulic fluid/fuel	Excellent, almost no swelling	It is usable, but long-term soaking needs to be verified.
Lubricating oil/cutting fluid	Excellent	good
Acids and bases (diluted)	Excellent	Generally, it is not resistant to strong alkalis.
strong base	good	Poor quality will be eroded.
Ketone/Ester Solvents	Some brands are restricted	better
Strong oxidizing agents such as concentrated sulfuric acid	impatience	impatience

“Usable” does not equal “recommended”. For any project involving long-term immersion, an immersion test must be conducted according to the actual medium and temperature to measure the expansion rate, mass change, and strength retention rate.

 

1. Radiation Resistance and Vacuum Gas Evolution: PI’s Home Ground

This is PI’s irreplaceable area, and the real source of its price premium.

Radiation tolerance: PI can reach a cumulative dose on the order of 10⁸ Gy, while PEEK is roughly on the order of 10⁷ Gy. This difference of one order of magnitude means the difference between “usable” and “unusable” in long-life satellite missions and nuclear environments.

Vacuum gas separation: Both can control total mass loss (TML) and condensable volatile matter (CVCM) according to ASTM E595, but PI has significantly more data accumulation and process maturity in the aerospace field, and is the default option for most satellite models.

Cryogenic: PI can withstand temperatures down to -269℃ (liquid helium temperature range) without becoming brittle, while the practical lower limit of PEEK is roughly between -60℃ and -100℃. PI is the only viable option for superconducting magnets, cryogenic pumps, and liquid hydrogen/liquid helium systems.

A useful judgment statement: If this wire is to be put into a vacuum tank, onto a cryogenic platform, or to calculate the total irradiation dose—no need to compare anymore, just go straight to PI.

 

1. Mechanical Properties: PEEK wins in terms of durability, while PI loses in terms of susceptibility to wear and tear.

This point is often overlooked, but it is often the real cause of failure on site.

PEEK is wear-resistant, creep-resistant, and fatigue-resistant, and does not require additional armor under dragging, vibration, and reciprocating bending. Its disadvantages are that it is relatively stiff (flexural modulus approximately 3.6 GPa), has a large minimum bending radius, and wiring in confined spaces requires advance calculation.

PI (polyimide) is flexible but has poor abrasion resistance; the film will wear down under continuous friction, making it unsuitable for cable chains, reciprocating motion, and suspended cabling without fixed support. During installation, protective sleeves, cable trays, or fixing clamps must be used.

 

1. Technology and Cost: This is often the deciding factor in whether a project can be implemented.

project	PEEK cable	PI cable
Molding method	High-temperature extrusion (360–400℃) allows for continuous large-scale production.	Thin film wrapping + sintering: many processes, slow speed.
Small batch customization	It requires a dedicated screw and temperature control, resulting in high start-up costs.	Relatively flexible, but with a high proportion of manual labor.
termination difficulty	Due to its high melting point, the peeling and heat-shrinking processes require specific parameters.	Moisture absorption requires baking and end sealing.
relative cost	high	Very high (typically 1.5–3 times that of PEEK).

Costs should be calculated over the entire lifecycle, not just the unit price. Here’s a real-world example: A high-temperature compartment originally used “silicone rubber insulation + fiberglass braiding + stainless steel armor,” requiring replacement every 18 months. Switching to PEEK increased the unit price by approximately 2.5 times, but extended the replacement cycle to over 5 years, and eliminated the armor layer, reducing weight by about 30%. The total cost over three years actually decreased. These kinds of calculations need to be presented to the customer.

 

7. The actual operating conditions of five TST CABLE PEEK and PI cables , providing direct judgment.

Operating Condition 1 | Aircraft engine compartment, long-term 220℃, in contact with hydraulic oil and fuel

The temperature is not within the necessary range for PI, but the dielectric environment is very harsh and requires wear-resistant and flexible wiring.

Judgment: PEEK. Using PI means paying for irradiation and cryogenic capabilities that are not actually used.

Operating Condition 2 | Low Earth Orbit Satellite Payload, Vacuum, Temperature Cycling -100°C to +120°C, Weight Reduction Required

The key constraint is not the upper temperature limit, but rather the amount of gas evolution that contaminates the optical components and the amount of gas per gram of weight.

Judgment: PI, and request the TML/CVCM test report according to ASTM E595.

Operating Condition 3 | Semiconductor diffusion furnace, long-term 300℃, cleanroom environment, no strong radiation

The temperature is close to the upper limit of PEEK, but the environment is clean, there is no medium, no need for deep cryogenics, and the usage is large and cost is sensitive.

Judgment: PEEK (select the high-temperature resistant grade and verify the long-term thermal aging data); if above 350℃ is required, switch to PI.

Operating Condition 4 | Oil well downhole, 150–200℃, long-term immersion in crude oil and mud, strong vibration

The temperature is not extreme, but the medium and mechanical stress are the main killers, and PI is not superior in terms of wear resistance and alkali resistance.

Judgment: PEEK; if necessary, construct a thick-walled or sheathed structure.

Operating Condition 5 | Superconducting magnet, liquid helium temperature range −269℃, requiring extremely low thermal conductivity and extremely small volume

Due to cryogenic conditions, space constraints, and the need for low heat leakage, PEEK has lost its practical flexibility at −269°C.

Judgment: PI, and the cold bending test report needs to be confirmed.

 

8. No need to choose one of two: Mixed structures are the more common answer.

In real-world projects, the optimal solution often involves using two materials simultaneously in a single line:

PI insulation + PEEK sheath: The inner layer is thin-walled for weight reduction, radiation resistance, and low gas evolution; the outer layer is wear-resistant, dielectric-resistant, and resistant to mechanical damage. This is the most common combination in aerospace and high-end equipment, and it is also the standard solution for “having both”.

PI insulation + PTFE sheath: slightly lower cost, slightly lower temperature resistance, suitable for mid-range aerospace and semiconductor equipment.

PEEK insulation + low smoke halogen-free sheath: Used in scenarios where both temperature resistance and low smoke halogen-free certification of the entire cable are required (such as local high-temperature areas inside rail transit equipment compartments).

 

9. Three most easily confused perceptions

Misconception 1: PI has a low density, therefore it is lighter.

That’s reversed. PI has a density of approximately 1.42, while PEEK has approximately 1.30. PI is lighter because its wall thickness can be made extremely thin; the comparison is based on the overall cable density in g/m, not the material density.

Misconception 2: PI has higher temperature resistance, so PI should be used in all high-temperature applications.

Temperature resistance does not equal operating condition resistance. PI is susceptible to abrasion, strong alkalis, and moisture absorption. In environments with oil contamination and vibration, PEEK at 250℃ is actually more reliable. Selection should be based on failure mode, not temperature ranking.

Misconception 3: The more expensive one is always better.

PI (Producer Injection) is typically 1.5–3 times more expensive, but the premium is for the three capabilities: irradiation, cryogenics, and weight reduction. Capabilities that are not used are simply pure cost.

 

10. Frequently Asked Questions

Are PEEK cables and PI cables interchangeable?

Electrically, it’s usually possible, but engineering-wise, it’s usually not. Interchangeability changes the bending radius, wear life, range of media resistance, and termination process. These changes are not visible on the drawings but will become apparent during assembly and service.

Why is termination process control necessary for PI cables?

Indium phthalate (PI) absorbs moisture from the environment, which can lead to hydrolysis at high temperatures, causing insulation delamination and a sharp drop in dielectric properties. Therefore, it requires dry storage, end sealing, matching potting materials, and a specified baking profile before soldering. This is not a quality issue, but an inherent property of the material, and must be addressed through process management.

How can I verify that a supplier’s PEEK cable is genuine PEEK?

Three steps: obtain the material grade and source; obtain the elongation at break retention rate after aging at 250℃ (pure PEEK and blends have a significant difference in this item); if necessary, perform DSC to measure the melting point, pure PEEK should be around 340℃.

Given such a large cost difference, under what circumstances is it worthwhile to include a Proforma Invoice (PI)?

It is worthwhile if any one of the three signals is met: there is a clear requirement for total irradiation dose; there is cryogenic operation below −100°C; and weight is a hard constraint (there is a clear cost per gram). When none of the three are met, PEEK is usually the more rational choice.

 

If you have any questions or needs, you can send us the project specifications, including temperature profiles, contact media, installation method (fixed/mobile), minimum bending radius, weight constraints, and target standards. We will then provide selection recommendations and a list of corresponding test reports.