Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
DuPont Pyralux FR: Flame Retardant Flex Laminates — UL Rated, Full Spec Guide
If your flex PCB design needs a UL flammability rating — and a growing number of industrial, telecommunications, and consumer product designs do — DuPont Pyralux FR is the material most fabricators are going to pull off the shelf. It fills a specific and well-defined role in the Pyralux family: acrylic-adhesive flex laminate with certified flame retardancy, built on Kapton polyimide film, processed just like Pyralux LF. This guide walks through the full FR product line, product codes, electrical and mechanical specs, processing notes, and honest comparisons to help you decide where FR belongs in your design — and where it doesn’t.
What Is DuPont Pyralux FR? The Core Value Proposition
DuPont Pyralux FR is a composite of DuPont Kapton polyimide film with copper foil on one or both sides, bonded together with a proprietary, flame-retardant, C-staged acrylic adhesive. Pyralux FR flexible composites are recommended for use in single-sided, double-sided, multilayer, and rigid-flex circuits that require flame retardancy.
That single sentence from DuPont’s own datasheet captures the product’s purpose precisely. It’s a three-layer construction — copper, flame-retardant acrylic adhesive, Kapton polyimide — and its defining characteristic is the UL 94 VTM-0 flammability certification. When your end product has to pass UL 796 or equivalent safety agency testing, and the flex circuit inside it is the component that needs the UL rating, Pyralux FR is your material.
The “FR” designation stands for Flame Retardant, not to be confused with the FR in “FR4” — which is fiberglass/epoxy territory. Pyralux FR is an all-flex material on Kapton film and processes through standard flex fabrication equipment. It is not a rigid PCB material.
For DuPont PCB applications where regulatory compliance drives material selection, Pyralux FR is DuPont’s commercial-grade answer for industrial and telecommunications applications requiring certified flame retardancy at a cost structure that makes production economics work.
The Full DuPont Pyralux FR Product Ecosystem
Like Pyralux LF, the FR series is a complete matched material ecosystem covering every functional layer in a flex PCB stack-up. This matters because you want consistent adhesive chemistry throughout your construction — mixing FR coverlay over LF laminate, for example, defeats the purpose of specifying flame-retardant materials if the UL certification is based on the full composite assembly.
Pyralux FR Copper-Clad Laminate (CCL)
The CCL is the base circuit substrate. Copper foil is bonded to one or both sides of Kapton polyimide film using the flame-retardant acrylic adhesive system. All copper-clad laminates are available with rolled-annealed (RA) copper or electro-deposited (ED) copper. In addition, both types are available with double-treated copper — nodules of electro-deposited copper on both sides of the copper foil — which, if used, eliminates surface preparation steps prior to resist or coverlay lamination.
That double-treated copper option is a real process efficiency gain in high-volume production. Skipping the surface prep step before coverlay lamination reduces cycle time and eliminates one source of surface contamination risk.
Pyralux FR Coverlay
Pyralux FR coverlay composites are constructed of DuPont Kapton polyimide film coated on one side with a proprietary flame-retardant B-staged acrylic adhesive. They are used to encapsulate etched details in flexible and rigid-flex multilayer constructions for environmental and electrical protection.
Critical note for designers: when the finished assembly requires UL certification, your coverlay must also carry the UL flame retardancy rating. Specifying standard Pyralux LF coverlay over FR laminate would leave the encapsulation layer uncertified — a problem that surfaces during UL testing and causes failures that are expensive to redesign around.
Pyralux FR Bondply
Bondply carries the same flame-retardant B-staged acrylic adhesive on both sides of the Kapton film. It is the interlayer bonding material for multilayer flex constructions. When you’re pressing a multilayer rigid-flex stack with FR materials throughout, bondply goes between each inner flex layer pair, maintaining the all-FR material chain from core to surface.
Pyralux FR Sheet Adhesive
Pyralux FR sheet adhesive is a proprietary flame-retardant B-staged modified acrylic adhesive coated on release paper. Sheet adhesive is used primarily to bond flexible innerlayers or rigid cap layers in multilayers. It can also be used to bond flexible circuits to rigid boards during the fabrication of rigid-flex circuits, as well as to bond stiffeners and heat sinks.
The flame-retardant formulation here is particularly important for rigid-flex assemblies where sheet adhesive is bonding the rigid FR4 cap layer to the flex core. If your product requires a full UL 94 rated construction, this bond layer needs to be FR-grade, not standard LF sheet adhesive.
DuPont Pyralux FR Product Codes and Construction Options
Understanding the FR part number system follows the same logic as Pyralux LF. The copper type suffix at the end of the product code tells you the foil specification:
Certified to IPC-4204/1: “Flexible Metal-Clad Dielectrics for Use in Fabrication of Flexible Printed Wiring.”
Pyralux FR Coverlay and Bondply Construction Options
Polyimide Thickness µm (mil)
Adhesive Thickness µm (mil)
IPC Certification
12 (0.5)
12, 25, 50, 75 µm
IPC-4203A/1
25 (1.0)
12, 25, 50, 75 µm
IPC-4203A/1
50 (2.0)
12, 25, 50, 75 µm
IPC-4203A/1
75 (3.0)
12, 25, 50, 75 µm
IPC-4203A/1
125 (5.0)
12, 25, 50, 75 µm
IPC-4203A/1
Pyralux FR Sheet Adhesive Product Codes
Product Code
Adhesive Thickness mil (µm)
IPC Certification
UL 94 VTM-0
FR0100
1.0 (25)
Yes
Yes
FR0200
2.0 (51)
Yes
Yes
FR0300
3.0 (76)
Yes
Yes
FR0400
4.0 (102)
Yes
Yes
FR1500
0.5 (13)
Yes
Yes
Sheet adhesive is certified to IPC-4203/18. FR0200 and FR0300 specifically meet UL 94 VTM-0 criteria per published test data.
Key Electrical and Mechanical Properties of Pyralux FR
The following data is based on typical values from DuPont’s official Pyralux FR datasheets. The reference construction for most published data is 1 oz RA copper / 1 mil adhesive / 1 mil Kapton.
Electrical Properties
Property
Typical Value
Test Method
Dielectric Constant (1 MHz)
3.5 max
IPC-TM-650 No. 2.5.5.3
Dissipation Factor (1 MHz)
0.04 max
IPC-TM-650 No. 2.5.5.3
Dielectric Strength
3,000 V/mil (118 kV/mm)
ASTM D-149
Surface Resistivity
10⁶ MΩ
ASTM D-257
Volume Resistivity
10⁹ MΩ·cm
ASTM D-257
Insulation Resistance
10⁷ MΩ
IPC-TM-650 No. 2.6.3.2
Mechanical and Thermal Properties
Property
Typical Value
Test Method / Standard
UL Flammability Rating
VTM-0
UL 94
Meets UL 796 Direct Support
Yes
UL 796
UL Maximum Operating Temp (MOT)
105°C
UL
Peel Strength (after lamination)
1.6 N/mm (9 lb/in)
IPC-TM-650 No. 2.4.9
Peel Strength (after soldering)
1.6 N/mm (9 lb/in)
IPC-TM-650 No. 2.4.9
Solder Float Resistance
Pass (10 sec at 288°C)
IPC-TM-650 No. 2.4.13
Adhesive Flow
10.0 mils/mil of adhesive
IPC-TM-650 No. 2.3.17.1
Dimensional Stability
Per IPC-4204/1
IPC-TM-650 No. 4.6.2
Multiple Lamination Cycles
No degradation
—
Refrigeration Required
No
Room temperature storage
Product Warranty
2 years from manufacture
—
A few specifics worth unpacking from an engineering perspective:
UL Maximum Operating Temperature of 105°C — this is the temperature at which UL has certified the material for continuous service. It’s set by the acrylic adhesive layer, not the Kapton film (which handles temperatures well above this). This is a key design constraint for any application with elevated steady-state operating temperature — vehicle interiors can approach this limit in worst-case summer scenarios, for example.
Peel strength of 1.6 N/mm maintained after soldering — this tells you the bond doesn’t degrade after the assembly reflow process. It’s an important qualification for any design where the flex circuit goes through an assembly soldering step before being installed in the final product.
Dissipation factor of 0.04 — same characteristic as Pyralux LF, driven by the acrylic adhesive layer. At frequencies below 1 GHz this is generally manageable. For designs pushing into higher frequency bands, this is the spec that would send you toward Pyralux AP or the TA/TK series materials.
UL Rating Explained: Why It Matters for Pyralux FR
The UL 94 VTM-0 rating is the specification that separates Pyralux FR from Pyralux LF in most design decisions. Understanding what this rating actually means prevents misapplication.
UL 94 is Underwriters Laboratories’ standard for flammability of plastic materials used in devices and appliances. The VTM-0 classification applies specifically to very thin materials (too thin for the standard vertical burn test) and requires that:
Flaming and glowing combustion stops within 30 seconds after each of five flame applications
No dripping of flaming particles that ignite cotton below the specimen
UL 796 Direct Support certification means the material is approved for use as a substrate in direct contact with current-carrying conductors — a requirement that many end-product certifications mandate for the PCB substrate itself.
UL Maximum Operating Temperature (MOT) of 105°C is the rated continuous service temperature. Products carrying a UL Recognized Component mark using Pyralux FR will reference this temperature rating in their UL file.
With a UL MOT of 105°C, FR is the product of choice for designs with UL 94 VTM-0 rating requirements — particularly in consumer power electronics, industrial controls, and telecommunications infrastructure where safety agency certification is non-negotiable.
DuPont Pyralux FR vs. Other Flex Laminates: Head-to-Head
Pyralux FR vs. Pyralux LF — The Key Tradeoff
Factor
Pyralux FR
Pyralux LF
Adhesive Type
Flame-retardant acrylic
Standard acrylic
UL 94 Rating
VTM-0
VTM-0*
Halogen-Free
No
Yes
RoHS Compliant
Yes
Yes
Processing
Identical to LF
Standard
UL MOT
105°C
105°C
Best For
UL-rated products
Halogen-free designs
Cost
Slightly higher than LF
Baseline acrylic cost
*Note: Pyralux LF also achieves VTM-0, but without the halogen-based flame retardant chemistry. The practical question is whether your supply chain, customer specification, or regional regulation requires halogen-free status — if yes, LF; if UL certification with no halogen restriction, FR is the validated path.
Pyralux FR vs. Pyralux AP — Performance vs. Certification
Factor
Pyralux FR
Pyralux AP
Construction
3-layer (adhesive-based)
2-layer (adhesiveless)
Loss Tangent
~0.04
~0.002
Tg (adhesive layer)
~100°C (acrylic)
220°C (polyimide)
UL Flammability
VTM-0
V-0 / VTM-0
Lead-Free Reflow
Use with care
Excellent
Fine Pitch Capability
Standard
High
Cost
Moderate
Higher
Primary Strength
UL certification, cost
High-frequency, high-reliability
The honest comparison: if your product has to carry a UL mark and cost constraints are real, Pyralux FR is the right specification. If your product is a military avionics box, a 5G mmWave module, or a multilayer rigid-flex medical instrument where reflow reliability over 10+ years is the design driver, Pyralux AP is the correct material and the cost premium is justified.
Industry Applications: Where Pyralux FR Gets Specified
Pyralux FR is a commercial-grade product ideal for industrial and telecommunications applications requiring flame retardancy. Here’s how that maps to specific use cases:
Industry / Application
Pyralux FR Role
Key Driver
Consumer power adapters and chargers
Flex circuit inside UL-listed power supply
UL 94 VTM-0 required for listing
Telecommunications infrastructure
Base station flex interconnects, switching equipment
UL 796 Direct Support compliance
Industrial controls and automation
Flex cable assemblies in control panels
Safety agency requirements
Office and home appliances
Internal flex connectors in UL-listed products
Product-level UL certification
LED lighting assemblies
Flexible circuit substrate for LED strips with UL mark
UL 94 VTM-0 + thermal resistance
Rigid-flex backplanes
Inner flex layers requiring flame retardancy
System-level fire safety standard
Automotive cabin electronics
Non-underhood flex interconnects in UL-certified modules
Moderate temperature, UL compliance
A practical note from the design side: one of the most common errors is specifying Pyralux LF for a product that eventually needs UL certification, then discovering during the listing process that the PCB material isn’t in the UL component database with the required rating. Catching this at the material selection stage — and specifying Pyralux FR from the start — prevents a costly material change late in development.
Fabrication and Processing Notes for Pyralux FR
Standard Lamination Conditions
Pyralux FR can be processed like Pyralux LF, which is a practical advantage if your fab shop already runs LF on its equipment. The standard press lamination parameters are:
Part Temperature: 182–199°C (360–390°F)
Pressure: 14–28 kg/cm² (200–400 psi)
Time: 1–2 hours at temperature
No specialized tooling or unique process chemistry is required beyond what a standard flex shop uses for Pyralux LF.
Adhesive Curing Behavior
The Pyralux FR acrylic adhesive is cured during the lamination step. The curing reaction does not produce any vapors, although impurities may volatilize. This is important to communicate to the press operator: unlike some prepreg systems that outgas significantly during cure, FR lamination doesn’t generate cure reaction by-products — but ambient impurities in the adhesive can volatilize, so adequate ventilation at the press is still standard practice.
Drilling and Routing
Provide adequate vacuum extraction around the drill head when drilling or routing. Polyimide and acrylic adhesive dust are respiratory irritants. Good practice from a quality standpoint as well: swarf contamination in drilled via holes before plating is a direct via reliability risk.
Storage
No refrigeration is required. Store at 4–29°C (40–85°F), below 70% relative humidity, in original packaging, kept dry and protected from physical damage. Shelf life is two years from date of manufacture under these conditions. A Certificate of Compliance (COC) and Certificate of Analysis (CoA) are available with every batch for traceability documentation.
Handling Safety
Pyralux FR flexible circuit materials do not contain polybrominated biphenyls (PBBs) or polybrominated biphenyl oxides (PBBOs), which is worth noting since these are specifically restricted under EU RoHS and REACH regulations. The flame retardancy is achieved through a different halogen-based chemistry that does not use these banned compounds. Personnel should wash hands before eating, smoking, or using facilities, and gloves should be changed daily when handling the material.
Quality, Certifications, and Traceability
DuPont manufactures Pyralux FR under a certified ISO 9001:2015 Quality Management System. Complete material and manufacturing records, including archive samples of finished product, are maintained by DuPont. Each manufactured lot is identified for reference traceability, with the packaging label serving as the primary tracking mechanism in the event of customer inquiry.
The relevant IPC certifications for Pyralux FR:
Product Type
IPC Certification
Copper-Clad Laminate
IPC-4204/1
Coverlay / Bondply
IPC-4203A/1
Sheet Adhesive
IPC-4203/18
A Certificate of Conformance is available with every batch for all certified constructions. For UL-related procurement, the UL file number for DuPont Pyralux FR materials should be confirmed directly with DuPont or your distributor — the specific file number is needed when populating UL component databases for your end product.
Useful Resources for Engineers Specifying Pyralux FR
Resource
Description
Link
DuPont Pyralux FR Official Page
Overview, full product listings, datasheet downloads
Frequently Asked Questions About DuPont Pyralux FR
Q1: What exactly does the UL 94 VTM-0 rating on Pyralux FR mean, and why is it required?
UL 94 VTM-0 is Underwriters Laboratories’ thin-material flammability classification. It requires the material to self-extinguish within 30 seconds after flame removal in vertical burn testing, with no dripping burning particles. Products that need to carry a UL listing — power supplies, industrial equipment, appliances, telecom hardware — typically need to demonstrate that internal PCB substrates meet this flammability standard. Pyralux FR achieves this through its flame-retardant acrylic adhesive formulation, making it the DuPont flex laminate of choice when UL certification is required on the end product.
Q2: Can DuPont Pyralux FR be processed with the same equipment as Pyralux LF?
Yes — this is one of the most practical advantages of the FR series. Pyralux FR can be processed exactly like Pyralux LF with identical lamination press parameters: 182–199°C, 14–28 kg/cm², 1–2 hours. If your fab shop is already qualified on Pyralux LF, adding FR to your approved materials list requires process qualification documentation but no capital equipment changes. This makes switching between LF and FR for different customer requirements relatively straightforward.
Q3: Does Pyralux FR contain polybrominated biphenyls (PBBs) or other banned flame retardants?
No. Pyralux FR materials do not contain polybrominated biphenyls (PBBs) or polybrominated biphenyl oxides (PBBOs). These specific compounds are banned under EU RoHS. The flame retardancy in Pyralux FR is achieved through a different halogen-based acrylic adhesive chemistry. Note, however, that Pyralux FR is not halogen-free — it does contain halogens as part of the flame retardant mechanism. If halogen-free compliance is a design requirement, specify Pyralux LF instead.
Q4: What IPC specifications should I reference on my fabrication drawing when calling out Pyralux FR?
Reference these IPC specs in your flex PCB fabrication notes depending on which FR component you’re specifying: copper-clad laminate to IPC-4204/1, coverlay and bondply to IPC-4203A/1, and sheet adhesive to IPC-4203/18. A typical fabrication note reads: “Base laminate: DuPont Pyralux FR per IPC-4204/1” with the specific product code and construction in the stack-up table. Your fabricator’s approved material list should confirm Pyralux FR as a qualified source for these specifications.
Q5: What is the UL Maximum Operating Temperature (MOT) of Pyralux FR, and how does it affect design?
The UL MOT for Pyralux FR is 105°C. This is the continuous service temperature at which UL has certified the material. It’s established by the acrylic adhesive layer, which softens as it approaches its glass transition temperature around 100°C. For UL-certified product designs, the thermal management analysis must confirm that the flex circuit operating temperature stays within this 105°C limit under worst-case conditions. Applications where the flex circuit runs close to this temperature — LED driver modules, motor drive flex interconnects, under-hood automotive connections — may need to upgrade to Pyralux AP or HT series materials to maintain both safety certification and long-term reliability.
Final Guidance: Specifying Pyralux FR Correctly
DuPont Pyralux FR occupies a clear and specific position in the flex laminate selection matrix. If your design checklist includes a UL flammability requirement, Pyralux FR is the answer. If it doesn’t — or if your specification requires halogen-free materials — Pyralux LF covers the same application space without the flame-retardant chemistry. If your design pushes above the 105°C UL MOT, or if signal integrity at multi-GHz frequencies is on the critical path, the discussion moves to Pyralux AP.
The mistake to avoid is using Pyralux LF by default and discovering late in the product development cycle that the UL listing process requires an FR-rated substrate. Material selection decisions made early are inexpensive. Material changes made during UL testing are not. Pyralux FR is a commercial-grade, broadly available, standard-process material — there’s no cost penalty for specifying it correctly from day one on any design that needs a UL-rated flex circuit.
Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
