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Polyimide, Aramid, PEEK, or Glass-Epoxy: Choosing EV Busbar Insulation
An EV pack's dielectric parts live in tight, hot, vibrating spaces where every tenth of a millimeter is negotiated. Choosing the insulation family is therefore a three-way conversation between thickness, temperature, and the way the part must wrap or carry load.
Polyimide film leads where a tight busbar wrap or thin underlay needs the most dielectric strength per unit thickness; aramid paper leads where the barrier must fold around complex geometry and shrug off handling; PEEK film takes the hot zones near power connections; glass-epoxy laminate is the answer when the dielectric part is also a structural plate; and mica covers the very-high-temperature corner where flame and isolation meet.
This guide compares the families the H-O busbar-insulation application page covers, with the governing methods named by designation: IEC 60243 and ASTM D149 for dielectric strength, IEC 60664 for the creepage-and-clearance framework, UL 94 for flame classifications, and FMVSS 305 at vehicle level. No kilovolt or CTI value is quoted for any grade; those live on the manufacturer's current data sheet at your gauge.
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The property landscape: through-thickness versus surface
The parent page splits every dielectric job into two halves, and the split shapes material choice. The through-thickness job is resisting breakdown across the barrier: governed by dielectric strength, a material property characterized per IEC 60243 / ASTM D149 that is grade- and thickness-specific.
The surface job is holding the required creepage and clearance: governed by geometry under the IEC 60664 framework, where working voltage, over-voltage category, pollution degree, and the material group (set by the comparative tracking index, CTI) decide the spacing.
A film can be superb through its thickness and still need folds and standoffs to deliver the surface distances; a rigid plate can hold spacing all day and be the wrong call where a wrap was needed. Most converted busbar parts serve both halves at once, which is why form factor leads the family comparison below.
The five families, by the decision each one wins
Polyimide film: the most dielectric strength in the least thickness
Polyimide film gives high dielectric strength in a very thin, foldable film, which makes it the lead for tight busbar wraps, thin underlays beneath bars, and interconnect isolation where the spacing budget is measured in fractions of a millimeter. It folds along die-cut score lines into three-dimensional sleeves, takes adhesive for peel-and-place installation, and holds its properties across the temperature range most pack electronics see.
Its dielectric strength, like every film's, is thickness- and method-dependent, so the value is confirmed per IEC 60243 / ASTM D149 on the current data sheet at your gauge.
Aramid paper: tough, conformable, fold-friendly
Aramid paper is the choice when the barrier must fold around a complex bar, survive assembly handling, or serve as a larger module interleaf. It is tougher and more conformable than film, tolerates creasing, and suits developed flat patterns that wrap multi-bend geometry. Where polyimide is picked for maximum withstand per micron, aramid is picked for the mechanical realities of a folded part that must be installed by hands or automation without splitting at the creases.
PEEK film: the hot-zone film
PEEK film takes over when the barrier runs hot, near a power connection or a joint that cycles with current, because it holds its properties where many films soften, and it adds chemical resistance. It is the targeted answer for the handful of locations in a pack where temperature, not thickness, is the binding constraint on a film.
Glass-epoxy laminate: the dielectric that carries load
Glass-epoxy laminate is the family for structural dielectric plates: busbar supports, rigid isolation barriers, and mounting plates that must isolate and bear load at once. It combines dielectric strength with mechanical strength and dimensional stability, machines cleanly with holes, slots, and counterbores, and can be faced with a film or paper where a thin high-dielectric surface layer is also wanted.
The trade is the obvious one: it is a rigid plate, not a wrap, and for a pure isolation barrier in tight space a film or paper is usually better and thinner.
Mica barrier sheet: where very high temperature joins the electrical role
Mica barrier sheet covers the corner where the dielectric job meets very high temperature or flame exposure, around busbars and terminals in thermal-event zones. Inorganic and non-combustible, it serves the high-temperature electrical barrier role films cannot, and because it is rigid and brittle it is typically laser- or waterjet-cut. Its dielectric duty, like every family's, is confirmed against the grade's own electrical data rather than assumed.
EV Busbar Insulation Families Side by Side
| Family | Dielectric strength per thickness | Folds / wraps | Hot-zone capability | Carries load | Typical busbar role |
|---|---|---|---|---|---|
| Polyimide film | Leads (thin film) | Scored folds | High for a film | No | Tight wraps, thin underlays |
| Aramid paper | Good | Tough, conformable | Good | No | Complex folds, module interleaves |
| PEEK film | High (thin film) | Film-like | Runs hot | No | Barriers near power connections |
| Glass-epoxy laminate | Plate-form | Rigid | Grade-dependent | Structural | Dielectric plates, busbar supports |
| Mica barrier sheet | Sheet-form | Rigid, brittle | Very high temp, non-combustible | Board form | High-temp electrical barriers |
Illustrative and relative only; confirm each grade on its current technical data sheet. Dielectric strength per IEC 60243 / ASTM D149 at your gauge; CTI and material group per the grade data; required creepage and clearance from the IEC 60664 tables applied to your design.
Form factor is half the specification
Converted dielectric parts succeed or fail on geometry as much as chemistry. A busbar wrap is rarely a flat rectangle: it is a developed flat pattern, die-cut with score lines and cut-outs, that folds into a sleeve around the bar and extends the surface path between conductors. A module interleaf is a large blank with clearance holes that must survive installation.
A structural plate carries counterbores and threads. H-O converts all three: die-cutting, kiss-cutting, scoring, and folding films and papers to developed patterns; machining and waterjet-cutting laminate plates; laminating a film or paper facing onto a plate where one part needs both a structural and a thin high-dielectric surface layer; and adding adhesive on a liner where peel-and-place beats loose parts.
The drawing review checks the fold radii against the material, the creep-path additions the folds provide, and the clearances at joints and terminals.
How H-O Products helps
H-O Products is a precision die-cut converter, not a raw-material producer. We do not extrude, cast, or mold the polyimide, aramid, PEEK, laminate, or mica; we buy film, paper, sheet, and laminate from the material manufacturers and convert them to your drawing: die-cut, kiss-cut, scored and folded, laser- and waterjet-cut, machined, laminated, slit, and kitted, with material traceability and lot-level data-sheet records under our ISO 9001:2015 certified quality management system.
We recommend a family and grade direction from your working voltage, temperature, geometry, and any flame requirement, and the grade-level dielectric strength and CTI are confirmed against the manufacturer's current data sheet; the governing creepage and clearance come from the IEC 60664 tables applied to your design.
Frequently asked questions
How do I choose between polyimide film and aramid paper for a wrap?
By the geometry and the handling. Polyimide leads where the wrap is tight and the spacing budget wants the most dielectric strength per unit thickness; it folds cleanly along die-cut score lines. Aramid paper is tougher and more conformable, so it leads where the part folds around complex geometry, survives rough handling, or serves as a large module interleaf. Many packs use both, each where its strength lies, with grade values confirmed per IEC 60243 / ASTM D149 on the data sheet.
When does the answer become a rigid plate instead of a film?
When the dielectric part must also carry a mechanical load or hold a precise position: structural dielectric plates, busbar supports, rigid isolation barriers. Glass-epoxy laminate combines dielectric and mechanical strength with dimensional stability and machines with holes, slots, and counterbores; it can also be faced with a film or paper where a thin high-dielectric surface layer is wanted. For a pure isolation barrier with no load and tight space, a film or paper is usually better and thinner.
Why is PEEK film specified in some locations instead of polyimide?
Temperature, mainly. PEEK holds its properties where many films soften, which suits barriers near power connections and joints that run hot with current, and it adds chemical resistance. It is a targeted choice for the hot zones rather than a wholesale replacement, and like every film its dielectric values are gauge-specific and confirmed on the current data sheet.
Can H-O certify a barrier to IEC 60664?
No, and the standard does not work that way. IEC 60664 is an insulation-coordination framework applied to a design: it sets the creepage and clearance your geometry must hold based on working voltage, over-voltage category, pollution degree, and the material group from the grade's CTI. A material supports the design with its dielectric strength and CTI, confirmed on its data sheet; the coordination result belongs to your design against the IEC 60664 tables, and H-O claims no creepage, clearance, or dielectric number.
Get a busbar-insulation material recommendation
Tell us the working voltage, the temperature, the geometry (wrap, interleaf, or plate), and any flame requirement, and we will recommend a family and grade direction and quote converted parts on your pattern.
Samples typically ship in 3 to 5 business days for common die-cut configurations; standard production runs about two weeks; special orders are quoted to the job. MOQ varies by material and part.
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Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- IEC 60243 and ASTM D149 (dielectric strength of solid insulating materials; thickness- and method-dependent).
- IEC 60664 (insulation coordination: working voltage, over-voltage category, pollution degree, material group / CTI).
- UL 94 (flammability classifications, grade- and thickness-specific); FMVSS 305 (vehicle-level electrical safety context).
- Manufacturer technical data sheets: polyimide film, aramid paper, PEEK film, glass-epoxy laminate, mica barrier sheet.
This article summarizes dielectric-material selection principles for EV busbar and pack insulation using the families and published methods named above. Comparisons are qualitative; no dielectric strength, CTI, creepage, or clearance value is stated for any grade or design, and grade-level values must be confirmed on the manufacturer's current technical data sheet at your gauge. The governing spacing comes from the IEC 60664 tables applied to your design.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter, not a raw-material producer, and does not certify the finished pack or vehicle.