Electrical Insulation Materials Fabricated for OEM and Industrial Equipment
“Electrical insulation” is a broad family — rigid laminates that carry structural load, flexible films you can fold into a battery box, papers that line a motor slot, and specialty composites engineered for arc and flame resistance. At Wm. F. McGraw & Co., we fabricate the full breadth of electrical insulation materials in-house at our Riverview, Michigan facility — cut to size, die cut, CNC machined, drilled, routed, and finished to your drawings. One supplier, one shop, one quote.
Below is the catalog. Each material family links to its dedicated specification page where one exists, with full properties, grades, and applications.
What Counts as Electrical Insulation?
Electrical insulation is any material engineered to prevent unintended current flow. In OEM design, that breaks into three functional roles:
- Dielectric isolation — preventing current flow between conductors. Dielectric strength (typically measured in volts per mil) is the key spec. Materials: most laminates, films, and papers in the catalog below.
- Structural insulation — isolating one component from another mechanically while also providing dielectric isolation. Examples: bus bar supports, standoffs, terminal boards. Materials: rigid thermoset laminates (G-10, FR-4, GPO-3, phenolic).
- Arc and flame protection — containing the consequences of an electrical failure. Examples: arc barriers in switchgear, flame-resistant enclosure liners. Materials: GPO-3, G-9, FR-4, and Formex®-class polypropylene.
Most production parts need more than one of these. A bus bar support holds a copper bar in place (structural), insulates it from ground (dielectric), and ideally contains an arc if the bar shorts (arc protection) — which is why GPO-3 dominates in switchgear and G-10 dominates in power electronics. The right material is the one that satisfies all the requirements your application actually has.
How do I get a quote?
Tell us what you’re building. We’ll come back with the right grade and the right fabrication approach for your application.
The Electrical Insulation Materials We Fabricate
A quick view of the catalog, organized by family. Detail and links to dedicated specification pages follow.
| Family | Form Factor | Examples We Fabricate | Typical Use |
|---|---|---|---|
| Rigid thermoset laminates | Sheet, rod, tube | G-10, FR-4, G-11, G-7, G-9, GPO-3 | Bus bar supports, standoffs, arc barriers, mounting panels |
| Flexible high-temp laminates | Sheet, roll | SG-200 polyester laminate | Wraps, perimeter mold insulation, motor wraps |
| Dielectric films | Roll, sheet | Kapton® polyimide, Mylar® PET, Teflon® PTFE | Slot liners, phase insulation, capacitor films |
| Flame-retardant polymer films | Sheet, roll | Formex®-class polypropylene (UL 94 V-0) | Battery insulators, enclosure barriers, surge shields |
| Aramid papers | Sheet, roll | Nomex®-class aramid paper (Type 410) | Motor slot liners, transformer interlayer insulation |
| Cellulose-based papers | Sheet, roll | Fish paper, vulcanized fibre | Economic insulation, gasketing, washers, spacers |
| Phenolic laminates | Sheet, rod, tube | Paper, canvas, linen phenolic | Mechanical-electrical parts (gears, bushings, structural) |
| Specialty composites | Sheet, block | Mica, mica-based plates, glass-mica composites | High-voltage motors, traction motors, generator coils |
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Rigid Thermoset Laminates
Rigid thermoset laminates combine fiberglass reinforcement with a thermoset resin to deliver dielectric strength and structural rigidity in the same part. This is the largest insulation family in our catalog, and one of WMF’s deepest specialties. We fabricate the full glass-laminate grade range — most fabricators stop at G-10 and FR-4.
G-10 is the standard glass-epoxy laminate — high dielectric strength, exceptional mechanical performance, and low moisture absorption. The workhorse for bus bar supports, standoffs, terminal boards, and structural insulators in switchgear and power electronics. FR-4 is G-10 with flame-retardant chemistry — same mechanical and dielectric performance, with the UL flame rating required for regulated enclosures and PCB substrates. G-11 is the high-temperature epoxy version, holding mechanical and dielectric performance where G-10 would soften.
When temperature climbs past what epoxy can handle, the resin system has to change. G-7 uses a silicone resin engineered for continuous service to roughly 428°F — used in generators, high-output motors, and arc shields. G-9 uses a melamine resin engineered specifically for arc and flame resistance — the go-to for arc barriers and switchgear panels where flashover is the primary risk.
GPO-3 sits in its own category. It’s a glass-polyester laminate with UTR (UL Tracking Resistance) arc and track resistance plus flame retardance — the dominant material for switchgear barriers, mounting plates, and transformer hardware. It’s been one of our deepest specialties for decades; the existing GPO-3 fabrication capability page covers our processing depth in detail.
Phenolic laminates — paper, canvas, and linen reinforced — round out the rigid family. They’re the older chemistry, but still the right answer for parts that need mechanical strength and electrical insulation at lower voltages, and where cost matters. Canvas phenolic in particular remains the standard for gears, bearings, and bushings in industrial mechanical equipment.
G-10 →
Standard glass-epoxy — structural + dielectric
FR-4 →
G-10 + UL 94 V-0 flame rating
G-11 →
High-temperature epoxy laminate
G-7 →
Continuous service to ~428°F
G-9 →
Melamine resin — arc and flame
GPO-3 →
Switchgear barriers, UTR rated
Flexible High-Temperature Laminates
SG-200 is a flexible glass-polyester laminate used where you need high-temperature insulation in a form that bends instead of breaks. Common applications include perimeter mold insulation, motor wraps, and transformer interlayer wraps. It’s often paired with Glastherm® HT on the same equipment — Glastherm handling the rigid platen and SG-200 handling the conformable perimeter wrap.
Dielectric Films
When the part needs to be thin and flexible — slot liners, phase insulation, capacitor barriers, flex circuits — the right material is a dielectric film. We work with the three industry standards.
Kapton® Polyimide Film
The high-temperature film. Handles continuous service to 400°F and intermittent exposure well above that. Excellent dielectric strength, very low film build, good chemical and abrasion resistance. The standard for traction motors, large DC motor coils, aerospace electrical systems, and any high-temperature application where thin profile matters.
Mylar® PET Film
The general-purpose dielectric film. Excellent dielectric strength at low cost, broad chemical resistance, good mechanical properties. Used in capacitors, motor slot insulation, transformer interlayer wraps, and general electrical insulation up to ~130°C continuous.
Teflon® PTFE Film
The specialty film. The right answer when chemical resistance, low friction, or extreme temperature range drives the spec — and where standard films can’t survive. Used in chemical-resistant electrical insulation, specialty cable construction, and high-frequency applications where Teflon’s low dissipation factor matters.
Flame-Retardant Polymer Films
ITW Formex®-class Polypropylene
Formex® and equivalent flame-retardant polypropylene films have replaced a lot of older fiber-based insulation in the past two decades. The material is lightweight, UL 94 V-0 rated, fold- and score-friendly (it supports living-hinge construction), highly resistant to moisture, and easy to die-cut, laser-cut, and form. Common applications include battery insulators (EV and industrial), surge shields in consumer electronics, compliance barriers in industrial enclosures, and air-flow ducting or baffles inside electronic enclosures. If your application currently uses fish paper or vulcanized fibre and you’ve never evaluated Formex-class polypropylene, it’s worth the conversation.
Aramid Papers
Nomex® Type 410 and Equivalent
DuPont introduced Nomex® aramid paper in the late 1960s and it remains the standard for high-temperature dielectric paper insulation. Inherent flame resistance, excellent thermal stability (continuous service to 220°C), high dielectric strength, and good resistance to acids, alkalis, solvents, and oils. The dominant material for motor slot liners, transformer interlayer insulation, and any electrical equipment where older paper materials can’t handle the operating temperature. Available in sheet and roll form; we die-cut, slit, and convert it to your spec.
Cellulose-Based Insulation Papers
Fish Paper
One of the oldest electrical insulation materials in continuous industrial use — vulcanized cellulose fiber paper with good mechanical properties and wear resistance. Light, durable, flexible, and economical. Still the right choice for low-voltage insulation, washers, spacers, and any job where cost is the deciding factor and the temperature and voltage don’t justify aramid paper.
Vulcanized Fibre
Thicker and more rigid than fish paper. Vulcanized fibre delivers excellent dielectric strength, high mechanical strength, and good wear resistance — often used for washers, spacers, gaskets, and structural insulation in motors, transformers, and electrical hardware.
Phenolic Laminates
Covered above with rigid thermoset laminates, but worth a callout in the insulation context. Phenolic laminates in paper, canvas, and linen reinforcements have been used as combined mechanical-and-electrical components for nearly a century. They remain the right answer when an application needs structural strength plus dielectric isolation at moderate voltage — gears, bushings, terminal boards, and low-voltage structural insulators.
Specialty Composites
Mica plates, glass-mica composites, and other specialty insulation are used where the standard materials don’t reach the operating envelope — particularly in large traction motors, high-voltage AC and DC motor coils, and generator stator construction. We work with these materials on a job-specific basis; if you’re designing high-voltage motor or generator components and need fabricated mica or specialty composite parts, contact us with your spec.
How to Choose the Right Electrical Insulation
Material selection comes down to matching your primary requirement to the material family engineered for it. The table below is a starting point — for any real-world application, send us the spec and we’ll narrow to one or two candidates.
| If your primary requirement is… | Start with… | Why |
|---|---|---|
| Structural rigidity + dielectric strength | G-10, FR-4, GPO-3 | Glass-laminate composites carry mechanical load and insulate |
| Flame retardance (UL 94 V-0) | FR-4, GPO-3, G-9, Formex® GK | All carry UL flame ratings; chosen by form factor |
| High continuous temperature (>250°F) | G-11, G-7, Nomex® Type 410, Kapton® | Resin or fiber chemistry holds at elevated temp |
| Arc and track resistance | GPO-3, G-9 | Engineered specifically for switchgear flashover environments |
| Thin, flexible, fold-and-form | Formex® polypropylene, Mylar®, Kapton® | Films score, fold, and bend without breaking |
| Motor slot or coil insulation | Nomex® Type 410, Mylar®, fish paper | Industry-standard slot and phase insulation |
| Low-cost gasket / washer / spacer | Fish paper, vulcanized fibre, paper phenolic | Economical for low-voltage and mechanical applications |
| Conformable wrap (mold or motor) | SG-200 flexible laminate | Flexible high-temperature alternative to rigid sheet |
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Three Principles That Apply Almost Universally
Match form factor to geometry first
Rigid parts get rigid laminates. Conformable parts get films or flexible laminates. The wrong form factor forces compromises on every other property.
Match temperature class to operating envelope, not nominal
An insulator running at its continuous-temperature limit ages much faster than one running 50°F below. Spec for the worst case.
Don’t over-spec
Kapton is right for traction motors; expensive overkill for a low-voltage washer that fish paper would handle. We’ll tell you when the cheaper material is the right material.
Key Properties to Specify
When you send us a spec, these are the properties that drive material selection. If your drawing doesn’t call them out, we’ll ask.
Dielectric strength (V/mil)
Maximum electric field the material withstands before breakdown. Higher is better; thicker sheet gives lower V/mil but higher absolute breakdown voltage.
Continuous service temperature
The temperature class the material sits at indefinitely without degrading. Rated by thermal class (B, F, H, N, R, 220, 240).
Comparative Tracking Index (CTI)
Resistance to surface tracking under voltage and contamination. GPO-3 and G-9 lead this category.
Flame rating (UL 94)
V-0 is the most stringent commonly specified rating. FR-4, GPO-3, G-9, and Formex GK all carry V-0.
Arc resistance
Time before a surface arc carbonizes the material into a conductive path. Critical for switchgear and high-voltage applications.
Moisture absorption
Lower is better for humid environments — affects dielectric strength over time. Glass-epoxy laminates and films lead; cellulose papers trail.
Mechanical strength and machinability
If the part is structural as well as insulating, this drives the choice between rigid laminate and softer film or paper.
Our Fabrication Capabilities
We fabricate every material above in-house at our Riverview, Michigan facility. We don’t quote it and ship it out — quality, lead time, and tolerance stay under our roof. For broader context on our thermoset processing depth, see our thermoset materials manufacturing capability page.
CNC Machining
Milling, drilling, tapping, routing, profiling for rigid laminates and phenolics.
Die Cutting
For films, papers, and thin laminates in production volumes.
Laser Cutting
Tight-tolerance flexible material conversion.
Waterjet & Saw Cutting
For thicker rigid laminates and specialty composites.
Slitting & Roll Converting
For films, papers, and flexible laminates.
Lamination
Pressure-sensitive adhesive, heat-activated film, multi-layer constructions.
Fastener Insertion
For assembled insulators and barriers.
Heat Forming
Shaped barriers, ducts, and three-dimensional parts.
Prototype to Production
Prototype quantities through repeat production runs.
On Material Selection
If you’ve inherited a design using fish paper, vulcanized fibre, or an older laminate grade, it’s worth asking whether the current material is still the right answer. Newer materials (Formex®-class polypropylene, FR-4, G-11) often deliver better dielectric performance, lower weight, and easier fabrication at competitive cost. We’ll tell you when an upgrade is justified — and when the original spec was already right.
Industries and Applications
We fabricate electrical insulation for OEMs across the industrial spectrum. Each industry links to its dedicated application page with material recommendations and case examples.
Switchgear →
GPO-3 barriers and mounting panels, G-9 arc barriers, FR-4 enclosures, fabricated viewing windows. The classic high-volume insulation application.
Transformers →
Laminate insulators (G-10, G-11), Nomex® aramid paper interlayer, fish paper economical spacers, GPO-3 structural insulators, mica composite for high-voltage.
Generators →
G-7 silicone laminate stator supports, G-10 terminal boards, Nomex® slot insulation, mica plate insulators for high-output machines.
Motor Applications →
Nomex® slot liners, Mylar® phase insulation, SG-200 motor wraps, phenolic structural supports, fish paper economical components.
Power Electronics →
G-10 and FR-4 bus bar supports, standoffs, terminal boards, Kapton® and Mylar® thin-profile insulators.
Electric Vehicles →
Battery insulators (Formex®-class polypropylene), structural composite supports, Kapton® thermal management barriers, FR-4 enclosure components.
Aerospace →
Kapton® film for high-temperature electrical systems, structural composites, dielectric components for cabin and avionics.
Medical →
Dielectric components for medical equipment, machined laminate parts, sterilizable insulators.
Oil and Gas →
Chemical-resistant insulation, high-temperature laminates, Teflon® film components for harsh-environment electrical systems.
Why OEMs Choose WMF McGraw for Electrical Insulation
Rigid and flexible, films and papers, the full glass-laminate family — fabricated under one roof in Riverview, Michigan.
Rigid and flexible, in one shop
Most insulation fabricators specialize in one form factor — either rigid laminates or flexible films and papers. We do both. That matters when your application uses both (switchgear, transformers, motors, EVs) and you’d rather not split the BOM across two suppliers.
The full glass-laminate family
Almost every competitor stops at G-10/FR-4 and GPO-3. We fabricate G-7, G-9, G-10, G-11, FR-4, and GPO-3 — the full grade range. If your application calls for a less-common grade, you don’t compromise on the material to find a fabricator.
Decades of GPO-3 specialty
GPO-3 fabrication for switchgear, transformers, and high-voltage hardware has been one of our deepest specialties for decades. Our GPO-3 capability page covers the processing depth in detail.
Material recommendation, not just quoting
Send us a drawing, a sample, or a description of the application — we’ll come back with material options, trade-offs, and a quote. If the part you specified isn’t the right material, we’ll tell you, before we cut the first piece.
In-house, under one roof
CNC machining, die cutting, laser cutting, roll converting, lamination, and finishing all happen at our Riverview, Michigan facility. We control quality, lead time, and tolerance ourselves.
Frequently Asked Questions
Quick answers about material selection, properties, fabrication, and quoting.
What’s the most commonly used electrical insulation material?
What’s the difference between dielectric strength and dielectric constant?
What does UL 94 V-0 mean?
Can you fabricate Formex® and Nomex®?
What’s the maximum operating temperature for electrical insulation?
Do you supply material only, or only fabricated parts?
Can you handle small prototype quantities?
How do I get a quote?
Request a Quote
Tell us what you’re building. Send your drawing or describe the application — we’ll come back with the right material recommendation and a quote, usually within one to two business days.
