Polyimide film sits at the high-performance end of the polymer spectrum. Few materials combine thermal endurance, electrical insulation, chemical resilience, and mechanical toughness in a single flexible, lightweight form — yet polyimide film does exactly that. It is routinely found in the wiring of spacecraft, the flex circuits of smartphones, the insulation of nuclear reactors, and the electrodes of medical biosensors.
This guide explains what polyimide film is, how it is made, what makes it perform so well, which grades are available, how it can be processed, and where it is being used today — including in emerging fields where its capabilities are still being fully explored.
What is Polyimide (PI) Film?
Polyimide (PI) is a class of polymer characterised by the imide linkage (-CO-N-CO-) in its backbone. When formed into a film, polyimide produces a thin, flexible sheet that is typically amber or golden-brown in colour, though transparent variants exist. The material is essentially infusible — meaning it does not melt below its decomposition temperature — which is one of the properties that distinguishes it from most other engineering polymers.
The polymer backbone consists predominantly of aromatic rings, which is the structural origin of its exceptional thermal stability. Aromatic polyimides are formed by a two-stage polycondensation reaction: a diamine and a dianhydride monomer are combined in a polar aprotic solvent to produce a polyamic acid precursor, which is then thermally or chemically imidised (cyclised) to form the final polyimide structure. The most commercially important variant, based on pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA), forms the backbone of DuPont's Kapton® product family.
The resulting polymer chain is rigid, planar, and highly conjugated, which accounts for the material's characteristic combination of stiffness, thermal resistance, and optical absorption in the visible range.
Key Properties of Polyimide Film
Understanding polyimide film means understanding each of its four core property families in detail.
Thermal Properties
Polyimide film maintains its mechanical and electrical properties across an exceptionally wide temperature range. Standard Kapton® HN film, for example, retains useful properties from −269°C (the temperature of liquid helium) to +400°C — a span of nearly 670°C. Most engineering polymers begin to soften or degrade well below 200°C. Polyimide does not melt; at temperatures above its useful upper limit it carbonises rather than flowing, which is a critical distinction in applications where dimensional stability under extreme heat is non-negotiable.
The coefficient of thermal expansion (CTE) for standard polyimide film is approximately 20 ppm/°C, though specific grades such as Kapton® EN are engineered to match the CTE of copper (around 17 ppm/°C), making them essential for flexible printed circuit substrates where thermal cycling would otherwise cause delamination or trace cracking.
Electrical Properties
Polyimide film is an outstanding electrical insulator. Its dielectric constant is approximately 3.4 at 1 MHz — low enough to minimise signal propagation delays in high-frequency circuits. Dielectric strength typically exceeds 200 kV/mm for standard film thicknesses, making it effective as an insulating barrier even in thin cross-sections. Volume resistivity is in the range of 10¹⁵ to 10¹⁷ Ω·cm, and the material shows excellent retention of these properties at elevated temperatures and under radiation exposure.
These electrical characteristics make polyimide film the substrate of choice wherever conventional FR4 PCB laminate would fail: high-temperature electronics, space-grade wiring harnesses, cryogenic instrumentation, and miniaturised flexible circuitry.
Mechanical Properties
Despite being thin and flexible, polyimide film has a tensile strength of approximately 170 MPa and a Young's modulus of around 2.5 GPa for standard grades — respectable figures for a polymer film. It resists tearing, puncture, and fatigue under repeated flexing, which is why it appears in dynamic flex-circuit applications where the circuit must survive millions of bend cycles.
Importantly, polyimide film retains its mechanical properties at cryogenic temperatures without becoming brittle — a failure mode that affects many other polymers. This makes it viable for applications in liquid nitrogen or liquid helium environments, including superconducting magnet systems and cryogenic sensor arrays.
Chemical Resistance
Polyimide film shows good resistance to most organic solvents, dilute acids, and oils. It is not attacked by jet fuels, hydraulic fluids, or the cleaning agents typically used in electronics manufacture. However, it is susceptible to concentrated strong alkalis and prolonged exposure to steam, both of which can hydrolyse the imide bond. In environments where alkaline exposure is unavoidable, surface coatings or alternative grades with enhanced moisture resistance should be specified.
The material also has very low outgassing behaviour under vacuum, making it suitable for use in space environments where volatile contamination of optical surfaces or sensitive instruments would be detrimental.
Radiation Resistance
Polyimide film's performance under ionising radiation deserves particular attention, as it is a significant differentiator from most competing polymer films. The aromatic backbone absorbs radiation energy without the degree of chain scission that affects aliphatic polymers. Kapton® HN, for instance, is routinely used in cable insulation around nuclear reactors and in beam diagnostics equipment at particle accelerators, where cumulative radiation doses would destroy PTFE or polyethylene insulation.
This inherent radiation tolerance is a property of the polyimide backbone shared across all Kapton® grades, rather than a characteristic of any single specialised formulation. Kapton® HN itself is therefore the standard choice for radiation-intensive applications including satellite sensor encapsulation, nuclear instrumentation, and biomedical electrode arrays where sterilisation by gamma irradiation must not compromise the film's electrical performance. Where specific grades are selected for demanding environments, the choice is typically driven by secondary requirements — for example, Kapton® HPP-ST for applications demanding tighter dimensional tolerances, or Kapton® HN in its standard form where broad-spectrum radiation hardness is the primary concern.
Processing and Fabrication
One of polyimide film's practical advantages is that it can be converted, modified, and integrated using a wide variety of standard processing techniques. This fabricability means engineers are not constrained to using the film in its as-supplied form.
- Cutting can be performed mechanically (die-cutting, slitting, laser cutting) to produce custom shapes and widths. Laser cutting is particularly well-suited to polyimide because the material ablates cleanly without melting, leaving precise, burr-free edges.
- Etching using alkaline solutions or plasma processes is used to create patterned features or to improve surface adhesion prior to metallisation or lamination.
- Coating with conductive inks, dielectric layers, or adhesives is straightforward. Polyimide film accepts a variety of coating systems and can be surface-treated by corona discharge or plasma activation to improve wettability where standard adhesion is insufficient.
- Laminating to copper foil, other polymer films, or adhesive layers produces the flexible copper-clad laminates (FCCL) used as the starting material for flex-circuit fabrication. The chemistry of the adhesive — or in the case of adhesiveless laminates, the direct bonding of copper onto the polyimide surface — determines the heat resistance of the assembly.
- Metallising by sputtering or evaporation deposits uniform thin-film metal layers for electrical, reflective, or shielding functions.
- Moulding and forming under heat and pressure can produce three-dimensional shapes from flat film for specific enclosure or protective component applications.
Goodfellow's polymer film transformation service can assist with many of these conversion processes, allowing customers to specify dimensions, coatings, or laminate structures tailored to their application rather than working around standard catalogue formats.
Metallised and Converted Forms
Polyimide film's utility extends well beyond the base film. Goodfellow supplies both aluminium-metallised polyimide film and metallised coils, in which a nanoscale aluminium coating (typically 30–80 nm) is deposited onto the polyimide surface by physical vapour deposition. This thin metal layer introduces controlled electrical conductivity and EMI shielding capability without meaningfully compromising flexibility or high-temperature performance.
Metallised polyimide film is used in thermal control blankets for spacecraft (the gold-coloured multi-layer insulation visible on satellites and probes), reflective thermal barriers in satellite systems, roll-to-roll manufactured flexible antennas, and conductive laminates in high-reliability sensor arrays. The thinness of the aluminium layer means the film retains its flexibility and can be wound onto rolls for continuous manufacturing processes.
Polyimide is also available from Goodfellow in tube form, providing a dielectric conduit geometry suitable for fuel-cell flow channels, fibre-optic cable protection, and aerospace or vacuum-grade conduit applications where the combination of dimensional precision, temperature resistance, and electrical insulation is required in a tubular form.
Applications by Industry
Aerospace and Space
Polyimide film was adopted by the space industry early and remains indispensable today. Its combination of thermal endurance, low outgassing, radiation resistance, and mechanical stability across cryogenic-to-elevated-temperature ranges makes it the dominant material for spacecraft wiring insulation, multi-layer insulation blankets (MLI), and onboard camera and sensor flex circuits. NASA and ESA missions have relied on Kapton®-insulated wiring for decades. Its documented ability to survive long-duration radiation exposure in the Van Allen belts and the more intense radiation environment of deep-space missions has made it the benchmark against which alternative insulating films are evaluated.
Electronics and Flexible Printed Circuits
The electronics industry consumes the largest volume of polyimide film globally. In flexible printed circuits, it serves as the dielectric substrate onto which copper signal traces are etched or plated. The combination of dimensional stability, CTE matching with copper, and soldering-temperature resistance makes it the only commercially practical substrate for fine-pitch high-density flex circuits at scale. It appears in smartphones, tablets, laptops, cameras, and wearables — anywhere the circuit must flex, fold, or conform to a non-planar geometry.
Beyond flex circuits, polyimide film is used in chip-scale packaging, where it forms thin dielectric layers between conductor levels in advanced semiconductor packages. It also appears as a substrate in flexible display manufacturing and as an insulating layer in solid-state sensor structures.
Automotive and Industrial
Modern vehicles contain polyimide film in sensors, motor winding insulation, and wiring harnesses in under-bonnet environments where temperatures exceed the rating of standard insulating materials. As automotive electronics increasingly migrate toward electrification — with battery packs, power electronics, and drivetrain motor controls all requiring insulation that performs reliably at elevated temperatures over a 15-year or greater service life — demand for polyimide film and related materials has grown substantially.
In industrial settings, it is used in motors, transformers, and generators as inter-turn and slot insulation where operating temperatures are elevated and space is at a premium. Its ability to maintain dielectric integrity under sustained thermal stress distinguishes it from polyester-based alternatives.
Medical and Biomedical
Polyimide's biocompatibility, chemical resistance, and ability to be fabricated into very thin, flexible structures have made it increasingly prominent in medical device construction. It is used as a substrate for implantable neural probes, EEG electrode arrays, and flexible biosensors where the device must conform to biological tissue without causing mechanical damage. The low impedance and biocompatibility demonstrated by CRC-grade electrodes in EEG applications are one specific example of this expanding use case.
It is also used in minimally invasive catheter and endoscope construction, where precision-formed polyimide tubing provides dimensional accuracy and kink resistance in tight-radius applications.
Energy: Solar and Fuel Cells
Polyimide film's thermal stability and flexibility make it a viable substrate for roll-to-roll deposited thin-film photovoltaic cells, where conventional rigid glass substrates would preclude the low-cost continuous manufacturing processes needed to drive down solar energy costs. Its durability under UV radiation and thermal cycling is central to long operational lifetimes in outdoor solar applications.
In fuel cell systems, polyimide components appear as insulating separators and as tube or film substrates supporting membrane electrode assemblies in miniaturised cell configurations.
Research and High-Energy Physics
At particle accelerator facilities, polyimide film appears as a beam diagnostic window, ion-beam imaging substrate, and cable insulation on systems that accumulate high radiation doses during operation. Its ability to maintain dimensional stability and dielectric performance under conditions that destroy conventional polymer insulation makes it the default choice in these environments. Cryogenic superconducting magnet systems — in both research accelerators and medical MRI machines — use polyimide film as the inter-layer insulation in magnet coil windings that operate at liquid helium temperatures.
Labelling in Harsh Environments
A less prominent but practically important application is printed labelling. When combined with appropriate printable coatings, polyimide film produces labels that survive extreme temperatures, chemical exposure, and abrasion that would destroy polyester or paper-based label materials. It is specified for component identification in aerospace assemblies, high-temperature industrial equipment, and chemical processing environments where label legibility must be maintained over long service lives.
Comparing Polyimide Film to Alternative High-Performance Films
Engineers specifying a dielectric film often evaluate polyimide against PTFE (polytetrafluoroethylene) and PEI (polyetherimide) films.
- PTFE offers lower dielectric constant and lower friction, and has superior resistance to aggressive alkalis and steam. However, it is significantly more expensive per unit area, substantially weaker mechanically, difficult to bond without special surface treatments, and — critically — cannot be laminated to copper using standard flexible circuit manufacturing processes. For most flex-circuit applications, polyimide is the only practical choice.
- PEI film (such as ULTEM®) offers better processability and slightly lower cost, but its upper continuous-use temperature is typically around 170°C compared to polyimide's 400°C, and it lacks polyimide's radiation resistance. For applications within its temperature range, PEI may be a cost-effective substitute; for aerospace, nuclear, or cryogenic applications, polyimide is the specification.
Processing and Selection Considerations
When specifying polyimide film for a particular application, several practical considerations should guide grade selection.
CTE matching is the first consideration for flex-circuit applications. If copper traces are to be bonded to the film and subjected to thermal cycling, selecting a grade with a CTE close to copper's — such as Kapton® EN — substantially reduces the risk of delamination or trace failure.
- Moisture sensitivity matters in high-humidity environments or where the film will be exposed to steam. Standard polyimide is hygroscopic to a modest degree, absorbing up to approximately 2.8% water by mass at equilibrium in a humid environment. This moisture uptake can marginally affect dimensional stability and dielectric properties. For applications where this is a concern, grades with reduced moisture absorption coefficients — such as HPP-ST — should be selected.
- Adhesion requirements determine whether surface treatment is needed. In its as-supplied form, polyimide film has a relatively low surface energy that can make bonding with standard adhesives unreliable. Corona discharge treatment, plasma activation, or chemical etching can substantially improve adhesion where required. Goodfellow's technical solutions team can advise on specific surface preparation protocols for particular bonding systems.
- Thickness selection affects both flexibility and dielectric withstand voltage. Standard catalogue thicknesses range from 8 µm to 125 µm. Thinner films offer greater flexibility and conformability; thicker films provide higher absolute dielectric strength and better mechanical robustness. The appropriate thickness depends on the specific bend radius, dielectric requirement, and mechanical load in the application.
Goodfellow's Polyimide Film Supply Capability
Goodfellow carries DuPont™ Kapton® polyimide film across multiple grades and a wide range of thicknesses, widths, and form factors — including standard sheets, rolls and coils, and precision-cut discs. The range includes both plain and aluminium-metallised variants, as well as polyimide tube for conduit applications.
With no minimum order quantity, 48-hour despatch on in-stock items, and access to Goodfellow's technical and polymer film transformation services, customers can obtain both standard catalogue formats and application-specific converted products from a single supplier with over 70 years of experience in advanced materials supply.
For applications requiring a specific thickness, surface treatment, or laminate configuration not available in the standard range, Goodfellow's materials customisation service provides a route to application-tailored solutions.
