DuPont Pyralux FR is a UL 94 VTM-0 rated flame-retardant flex laminate built on Kaptonยฎ polyimide film. This complete spec guide covers copper-clad laminates, coverlays, bondplys, sheet adhesives, lamination parameters, IPC certifications, product codes, and how FR compares to other Pyralux grades โ everything a PCB engineer needs before specifying this material.
Keyword focus: DuPont Pyralux FR | Word count: ~2,000 | Last updated: 2026
If you’re designing a flexible or rigid-flex PCB and the end product needs to pass UL flammability certification, DuPont Pyralux FR is almost certainly going to land on your material shortlist. It’s one of those base materials that PCB engineers treat as a known quantity โ well-documented, IPC-certified, and genuinely reliable when you process it correctly. This guide breaks down everything from construction and product codes to lamination parameters, IPC certifications, and how the FR family stacks up against other Pyralux grades.
What Exactly Is DuPont Pyralux FR?
DuPont Pyralux FR copper-clad laminate is a composite of DuPont Kaptonยฎ polyimide film with copper foil on one or both sides, bonded together with a proprietary, flame-retardant, C-staged acrylic adhesive. The “FR” in the name stands for Flame Retardant โ and that’s the defining characteristic that separates this product line from the standard Pyralux LF series.
Pyralux FR products are acrylic-based flame retardant copper-clad laminates, coverlays, bondplys, and sheet adhesives for products requiring UL rating. In practice, that means if your customer’s end product needs to carry a UL 94 flammability mark, FR is the grade you reach for.
The product family is broader than just the copper-clad laminate. It covers four distinct material types, each playing a different role in flex and rigid-flex stack-ups:
- Copper-Clad Laminate (CCL)ย โ the core circuitry substrate
- Coverlayย โ protective encapsulant over etched copper features
- Bondplyย โ adhesive-coated film for bonding inner layers or cap layers
- Sheet Adhesiveย โ standalone adhesive film for bonding stiffeners, heat sinks, or rigid cap layers
Understanding which of these you need โ and when โ is one of the first decisions you make when laying out a Pyralux FR stack-up.
Why the Flame Retardant Rating Matters
Not every flexible circuit needs a UL flame-retardancy rating. Consumer electronics for internal use sometimes get away without it. But the moment your design goes into a product that needs UL 796 component recognition, or a device that passes through UL 94 testing, the laminate material must support that certification.
DuPont Pyralux FR carries a UL 94 VTM-0 flammability rating and a UL maximum operating temperature (MOT) of 105ยฐC. VTM-0 is the highest classification under the UL 94 thin-material test standard โ it means the material self-extinguishes rapidly and does not drip burning particles. For most applications where a UL listing is required, VTM-0 is exactly what the standard demands.
From a safety compliance standpoint, Pyralux FR flexible circuit materials do not contain polybrominated biphenyls (PBBs) or polybrominated biphenyl oxides (PBBOs), which keeps the material aligned with RoHS and REACH requirements โ no surprises when your product hits EU customs.
DuPont Pyralux FR Product Codes: Reading the Part Number System
One thing that trips up newer engineers is the Pyralux FR part number system. Here’s how to decode it.
Add “R” to the end of the code to specify rolled-annealed copper (e.g., FR9210R). Add “E” to the end to specify electro-deposited copper (e.g., FR9210E). If rolled-annealed double-treated copper is specified, add the letter “D” to the end of the product code (e.g., FR9210D).
The double-treated copper option is worth noting. Double-treated copper (nodules of electro-deposited copper on both sides of the copper foil) eliminates surface preparation steps prior to resist or coverlay lamination. If you’re running high-volume production and want to skip an oxide treatment step, specifying the “D” suffix can reduce your process complexity.
Copper-Clad Laminate Thickness Options
| Kaptonยฎ Film Thickness | Available Copper Weights | Copper Type |
| 1 mil (25 ยตm) | ยฝ oz, 1 oz | RA or ED |
| 2 mil (50 ยตm) | ยฝ oz, 1 oz, 2 oz | RA or ED |
| 3 mil (75 ยตm) | ยฝ oz, 1 oz, 2 oz | RA or ED |
| 5 mil (125 ยตm) | ยฝ oz, 1 oz, 2 oz | RA or ED |
Rolled-annealed (RA) copper is the standard recommendation for dynamic flex applications because it has a finer grain structure and better fatigue resistance under repeated bending. ED copper is more common in static flex or rigid-flex applications where cost is a priority.
Coverlay and Bondply Specifications
Pyralux FR coverlay and bondply composites are constructed of DuPont Kaptonยฎ polyimide film, coated on one side (both sides for bondply) with a proprietary B-staged acrylic adhesive. They are used to encapsulate etched details in flexible and rigid-flex multilayer constructions.
Coverlay / Bondply Construction Options
| Polyimide Thickness | Adhesive Thickness | IPC Certification |
| 12 ยตm (0.5 mil) | 12 ยตm | IPC 4203A/1 |
| 25 ยตm (1 mil) | 25 ยตm | IPC 4203A/1 |
| 50 ยตm (2 mil) | 50 ยตm | IPC 4203A/1 |
| 75 ยตm (3 mil) | 75 ยตm | IPC 4203A/1 |
| 125 ยตm (5 mil) | โ | IPC 4203A/1 |
When selecting coverlay thickness, the adhesive layer needs to be thick enough to flow around your copper features and encapsulate them fully without voids. A general rule most fabricators follow: the adhesive thickness should be at least equal to your copper weight. For 1 oz copper (35 ยตm), a 50 ยตm adhesive coverlay is a safe minimum.
Sheet Adhesive Specifications
The Pyralux FR sheet adhesive is a standalone B-staged acrylic film coated on release paper. Sheet adhesive is used primarily to bond flexible innerlayers or rigid cap layers in multilayer lamination. It is also widely used to bond flexible circuits to rigid boards during the fabrication of rigid-flex circuits, as well as to bond stiffeners and heat sinks.
Sheet Adhesive Thickness Options
| Adhesive Thickness | IPC Certification | Typical Use Case |
| 12 ยตm (0.5 mil) | IPC 4203A/18 | Thin rigid-flex bonds |
| 25 ยตm (1 mil) | IPC 4203A/18 | Standard rigid-flex bonding |
| 50 ยตm (2 mil) | IPC 4203A/18 | Stiffener attachment |
| 75 ยตm (3 mil) | IPC 4203A/18 | Heat sink bonding |
| 100 ยตm (4 mil) | IPC 4203A/18 | Heavy stiffener / thick rigid bonds |
Lamination Processing Parameters
Getting the lamination right is where Pyralux FR either performs brilliantly or causes headaches. The C-staged acrylic adhesive has specific flow and cure requirements that you cannot shortcut.
Lamination conditions call for 14โ28 kg/cmยฒ (200โ400 psi) at 182โ199ยฐC (360โ390ยฐF) for 1โ2 hours at temperature.
Lamination Parameter Summary
| Parameter | Minimum | Typical | Maximum |
| Temperature | 182ยฐC (360ยฐF) | 185ยฐC (365ยฐF) | 199ยฐC (390ยฐF) |
| Pressure | 14 kg/cmยฒ (200 psi) | 21 kg/cmยฒ (300 psi) | 28 kg/cmยฒ (400 psi) |
| Time at temperature | 1 hour | 1.5 hours | 2 hours |
A few practical notes from the process side: use a vacuum press where possible to prevent void entrapment under the coverlay. The acrylic adhesive flows aggressively at the upper end of the temperature range, which can cause squeeze-out into circuit features if you’re not careful with your dam design. Stay in the middle of the parameter window unless your stack-up demands otherwise.
Pyralux FR can be processed like Pyralux LF. If you’re a shop that already runs LF material, your existing process documentation needs only minor adjustments for the FR grade.
Key Performance Properties
Here’s a consolidated look at the electrical and mechanical properties that matter most when you’re working with Pyralux FR in a design or fabrication context.
Pyralux FR Core Property Summary
| Property | Typical Value | Test Method |
| Flammability | UL 94 VTM-0 | UL 94 |
| Max Operating Temp (UL MOT) | 105ยฐC | UL 796 |
| Dielectric Constant (1 MHz) | ~3.5 | IPC-TM-650 2.5.5.3 |
| Dissipation Factor (1 MHz) | ~0.02โ0.03 | IPC-TM-650 2.5.5.3 |
| Peel Strength (Cu on Kapton) | โฅ 6 N/cm (โฅ 1.4 lb/in) | IPC-TM-650 2.4.9 |
| Dimensional Stability | ยฑ 0.10% | IPC-TM-650 2.2.4 |
| Volume Resistivity | โฅ 10ยนยณ ฮฉยทcm | IPC-TM-650 2.5.17 |
| Moisture Absorption | โค 2.0% | IPC-TM-650 2.6.2 |
The dielectric constant of ~3.5 is higher than adhesiveless all-polyimide laminates like Pyralux AP (Dk ~3.4), but for the majority of Pyralux FR applications โ consumer electronics, industrial controls, medical devices needing UL compliance โ this is entirely acceptable. If you’re pushing signals above 5 GHz through dynamic flex layers, that’s a different conversation.
Pyralux FR vs. Other Pyralux Grades: Which One Do You Actually Need?
Engineers sometimes default to Pyralux FR out of habit, when another grade might serve the design better (or be less expensive). Here’s a quick comparison:
| Grade | Adhesive System | Flame Rating | Max Op. Temp | Best For |
| Pyralux FR | Acrylic (C-staged) | UL 94 VTM-0 | 105ยฐC | Applications requiring UL rating |
| Pyralux LF | Acrylic (B-staged) | Non-rated | 105ยฐC | High-reliability consumer electronics |
| Pyralux AP | Adhesiveless (all-PI) | UL 94 V-0 | 180ยฐC | Aerospace, military, high-temp |
| Pyralux AG | Adhesiveless (all-PI) | UL 94 V-0 | ~150ยฐC | High-volume consumer, automotive |
The main reason to choose FR over LF is straightforward: UL certification requirement. If your product does not need UL, LF is often preferable because it has a longer industry track record in consumer applications and the B-staged adhesive is slightly more forgiving in processing. If you need temperatures above 105ยฐC continuously, neither FR nor LF is your answer โ you need AP or AG.
Quality, Storage, and Traceability
DuPont Pyralux FR Copper-Clad Laminate is manufactured under a certified ISO9001:2015 Quality Management System facility. A Certificate of Conformance is available with every batch. Complete material and manufacturing records for each lot, with samples of finished product, are retained for reference purposes.
Key features include: no refrigeration required for storage and a two-year product performance warranty. The no-refrigeration requirement is a practical advantage over some competing materials โ you can store Pyralux FR at room temperature in its original sealed packaging without complex cold chain logistics.
The roll labels carry lot number, DuPont order number, IPC specification, and customer part number. Hold onto those labels. If you ever have a field issue and need to trace back to a specific production lot, that label is your starting point.
Typical Application Areas for DuPont Pyralux FR
Where does Pyralux FR show up most often in real products?
Consumer electronics โ handheld devices, wearables, and display assemblies where UL 94 flammability marking is specified by the retailer or insurance underwriter.
Industrial controls and instrumentation โ panel-mount devices, sensor interfaces, and PLCs where IEC and UL safety certifications are standard requirements.
Medical devices โ class II medical equipment where UL 796 recognition of the circuit material is part of the regulatory submission package. (Note: Pyralux FR is not approved for permanently implanted devices.)
Automotive โ lower-temperature applications such as infotainment, interior lighting flex cables, and dashboard assemblies. For high-temperature underhood locations, AP or AG is the better call.
Telecommunications โ handset and base station assemblies requiring consistent UL-rated flex substrates in volume production.
For more on how DuPont PCB materials translate into fabricated boards across these industries, RayPCB has detailed fabrication guides that walk through stack-up design and material selection.
Useful Resources and Data Downloads
Here are direct links to official documentation and trusted third-party resources for DuPont Pyralux FR:
| Resource | Type | Link |
| Pyralux FR Copper-Clad Laminate Datasheet | Official DuPont PDF | epectec.com |
| Pyralux FR Coverlay Datasheet | Official DuPont PDF | epectec.com |
| Pyralux FR Bond Ply Datasheet | Official DuPont PDF | qnityelectronics.com |
| Pyralux FR Sheet Adhesive Datasheet | Official DuPont PDF | insulectro.com |
| Qnity/DuPont Laminates Overview | Product Portfolio Page | dupont.com |
| IPC-4204/1 Specification | IPC Standards | ipc.org |
| IPC-TM-650 Test Methods | IPC Test Methods | ipc.org |
| UL Product iQ Database | UL Certification Search | iq.ul.com |
Frequently Asked Questions About DuPont Pyralux FR
1. What is the difference between Pyralux FR and Pyralux LF?
Both are acrylic-based flex laminates using Kapton polyimide film. The critical difference is flammability: FR uses a flame-retardant C-staged adhesive formulation that earns a UL 94 VTM-0 rating, while LF (Low Flow) uses a standard B-staged acrylic and does not carry a UL flammability rating. If your product’s UL listing requires a rated laminate, FR is the correct choice. If it doesn’t, LF may offer slightly better adhesive flow control during lamination.
2. Does DuPont Pyralux FR require refrigerated storage?
No. One of the practical advantages of FR over some competitive materials is that it does not require cold storage. It should be kept in its original sealed packaging at controlled room temperature (typically 18โ25ยฐC), away from UV light and humidity. DuPont provides a two-year performance warranty under proper storage conditions.
3. Can Pyralux FR be used for dynamic flex applications?
Yes, but with caveats. The acrylic adhesive layer adds stiffness compared to adhesiveless constructions like Pyralux AP. For dynamic flex zones with very high cycle counts (millions of flex cycles), most engineers prefer adhesiveless laminates. For moderate flexing (thousands of cycles) with a UL rating requirement, FR is a practical and proven solution โ especially with rolled-annealed copper specified.
4. What IPC specifications does Pyralux FR comply with?
The copper-clad laminate is certified to IPC-4204/1. Coverlays and bondplys are certified to IPC 4203A/1. Sheet adhesives are certified to IPC 4203A/18. These certifications are important when your fabrication shop or customer requires IPC-compliant material on their traveler documentation.
5. Is Pyralux FR RoHS and REACH compliant?
Yes. Pyralux FR does not contain polybrominated biphenyls (PBBs) or polybrominated biphenyl oxides (PBBOs), keeping it compliant with both RoHS and REACH regulations. Always request the latest Material Safety Data Sheet (MSDS) and RoHS declaration from your distributor for specific lots, especially if you’re submitting compliance documentation for EU market entry.
Final Thoughts
DuPont Pyralux FR is the go-to material when your flex circuit needs UL flammability certification and you want a substrate with decades of real-world production history behind it. The acrylic adhesive system is familiar to most flex fabricators, the processing parameters are well-documented, and the IPC certifications line up cleanly with most procurement and quality requirements.
The trade-off versus adhesiveless grades like AP is primarily thermal ceiling (105ยฐC vs. 180ยฐC) and dynamic flex performance. For the vast majority of consumer, medical, and industrial applications where UL rating is required and temperatures stay below 105ยฐC, Pyralux FR is a reliable, cost-effective, and thoroughly vetted solution.
When you’re specifying it, always confirm the copper type (RA vs. ED), the adhesive thickness relative to your copper weight, and whether the end-product UL listing requires the VTM-0 rating specifically or will accept V-0 from a different test method. Get those three things right at the design stage and your fabricator will thank you.
For fabrication guidance and PCB prototyping using DuPont flex materials, visit RayPCB’s DuPont PCB resource page.
