Both 3240 and FR4 are epoxy glass fiber laminates used extensively in electrical insulation and structural applications. On paper they appear nearly identical — woven fiberglass cloth bonded with epoxy resin, cured under heat and pressure into rigid sheets, rods, and tubes. In practice, however, the differences between them are consequential enough to affect compliance, service life, and sourcing cost.
This article provides a technically grounded, buyer-focused comparison of 3240 and FR4 epoxy sheets. Whether you are an insulation system designer selecting materials for a transformer, a procurement engineer evaluating supplier offers, or a production manager standardizing your laminate inventory, this guide will help you understand where each material excels, where it falls short, and how to make the right specification decision for your application.
What Are 3240 and FR4 Epoxy Sheets?
Before comparing the two grades, it is worth establishing precisely what each material is and where its designation originates.
3240 epoxy glass sheet is a Chinese national standard (GB/T) designation for a woven glass cloth laminate bonded with epoxy resin. The “3240” code reflects the Chinese electrical insulation classification system. It is functionally equivalent to the NEMA G10 grade and the IEC 60893 designation EPGC 201. It is not inherently flame-retardant and is rated for continuous operating temperatures up to approximately 130°C (Class B insulation). The comprehensive guide on everything you need to know about 3240 epoxy sheet covers its full specification, grade variants, and standard equivalences in detail.
FR4 is a NEMA LI-1 designation for a woven glass cloth epoxy laminate that includes a halogenated or halogen-free flame-retardant additive, enabling it to achieve UL 94 V-0 flame classification. The “FR” prefix stands for Flame Retardant. FR4 shares the same base thermal class as 3240 (approximately 130°C continuous) but adds mandatory flame retardancy — a property that is required by code in many electrical enclosure, PCB, and panel applications.
SIDA supplies both 3240 epoxy glass sheet, tube, and rod and FR4/G10 epoxy glass sheet, tube, and rod across a full range of thicknesses and form factors for industrial and electrical applications.
Side-by-Side Property Comparison
The table below summarizes the most critical performance parameters for 3240 and FR4 in the context of electrical insulation applications:
| Property | 3240 Epoxy Sheet | FR4 Epoxy Sheet |
|---|---|---|
| Standard / Designation | GB/T; equivalent to NEMA G10, IEC EPGC 201 | NEMA LI-1 FR4; IEC EPGC 202 |
| Flame Retardancy | None — not rated | UL 94 V-0 compliant |
| Thermal Class | Class B (~130°C continuous) | Class B (~130°C continuous) |
| Dielectric Strength (⊥) | ≥14 MV/m (typical) | ≥14 MV/m (typical) |
| Flexural Strength (lengthwise) | ≥340 MPa | ≥340 MPa |
| Water Absorption (24h) | ≤0.20% | ≤0.10% |
| Machinability | Excellent — drills, mills, cuts cleanly | Good — slight additional tool wear from FR additives |
| Typical Cost | Lower | Higher (FR additive cost premium) |
| Primary Use Cases | Transformer components, motor insulation, structural parts | PCB substrates, switchgear panels, flame-rated enclosures |
At first glance, the two materials appear nearly equivalent in electrical and mechanical performance. The practical divergence is concentrated in three areas: flame retardancy, water absorption, and application compliance requirements — all of which are explored in the sections that follow.
Advantages of 3240 Epoxy Sheet
3240 is not simply a lower-cost substitute for FR4. In many electrical insulation applications, it is the technically preferable choice. Its key advantages include:
Superior machinability. Because 3240 does not contain flame-retardant additives — which can be abrasive to cutting tools — it machines more cleanly than FR4. For transformer components requiring close-tolerance drilling, milling, and turning, 3240 delivers lower tool wear and cleaner edge quality. This is a meaningful production cost factor for high-volume precision components.
Lower material cost. The absence of flame-retardant additives makes 3240 less expensive than FR4 at equivalent thickness and glass content. For structural insulation applications in oil-immersed transformers or motor end-plates where flame retardancy is not required by design or code, 3240 provides the same functional performance at a lower unit cost.
Established compatibility with transformer oil. 3240’s epoxy-glass construction exhibits reliable dimensional stability and chemical resistance in oil-immersed environments. It is a widely accepted material for spacers, support blocks, and structural components inside oil-filled transformers, where it has a long engineering track record.
Wide availability in Chinese supply chains. As a GB/T-standardized product, 3240 is produced by a large number of Chinese manufacturers to well-understood specifications. Procurement lead times and minimum order quantities tend to be more flexible than for specialty FR4 grades. For buyers managing global transformer supply chains, this is a meaningful sourcing advantage. For context on how Chinese and international laminate supply chains compare, the article on transformer supply chains in China vs international markets provides useful strategic perspective.
Disadvantages of 3240 Epoxy Sheet
Despite its advantages, 3240 is not universally applicable. Its limitations matter in specific regulatory and environmental contexts:
No flame retardancy. This is the fundamental limitation of 3240 in applications governed by fire safety codes. In switchgear enclosures, PCB substrates, control panels, and any equipment requiring UL, IEC, or national flame classification compliance, 3240 is not a compliant material. Specifying it in these contexts is not merely a performance risk — it is a regulatory non-compliance that can affect equipment certification and insurance liability.
Higher water absorption than FR4. 3240 typically exhibits water absorption up to 0.20% after 24 hours, compared to FR4’s 0.10% or lower. In high-humidity or outdoor environments, this difference can be significant over time. Absorbed moisture degrades surface resistivity and can initiate partial discharge in high-voltage applications. FR4’s lower absorption makes it the safer choice for equipment exposed to condensation or variable humidity conditions.
International standard recognition. While 3240 is recognized under Chinese GB/T standards and functions as a G10 equivalent, some international procurement specifications explicitly require NEMA LI-1 or IEC 60893 grade designations. In these situations, 3240 may require additional supplier documentation to demonstrate cross-standard equivalence, adding friction to the qualification process.
Advantages of FR4 Epoxy Sheet
FR4’s design rationale centers on flame retardancy, but this single property has broad implications for where and how it can be applied:
UL 94 V-0 flame classification. FR4 self-extinguishes when the ignition source is removed, meeting the requirements of UL 94 V-0. This certification is mandatory for PCB substrates in consumer electronics, industrial control panels, switchgear internal barriers, and any electrical equipment subject to IEC 60950, UL 508A, or equivalent standards. In these contexts, FR4 is not an option — it is the specification baseline. The guide on why FR4 material is commonly used in PCB fabrication explains the technical and regulatory logic behind this requirement.
Lower water absorption. FR4’s tighter water absorption limit (typically ≤0.10%) gives it better long-term surface insulation resistance in humid environments. For switchgear, outdoor enclosures, and equipment subject to condensation cycles, this property directly affects the insulation system’s long-term reliability.
International standard alignment. FR4 is explicitly defined under NEMA LI-1 and recognized under IEC 60893 as EPGC 202. For procurement teams operating under international engineering specifications, this alignment simplifies the documentation and qualification process with end-customers and certification bodies.
Broad global supply availability. FR4 is produced worldwide by a large number of certified manufacturers. Its widespread use in PCB manufacturing has driven consistent quality standards across the global supply chain, making supplier qualification relatively straightforward for buyers with established IPC or NEMA specification frameworks.
Disadvantages of FR4 Epoxy Sheet
FR4 is the correct specification in many applications, but it carries trade-offs that matter in certain contexts:
Higher cost. Flame-retardant additives — whether halogenated or halogen-free — add material cost. For structural insulation applications in oil-immersed transformers where flame retardancy provides no functional benefit, specifying FR4 over 3240 represents an unnecessary cost premium.
Marginally more difficult to machine. The abrasive nature of some FR additives accelerates tool wear during drilling and milling operations. For high-volume precision machined components, this translates to higher tooling costs and shorter cutting tool service life compared to machining 3240. Engineers managing transformer component production lines with large quantities of drilled and milled laminate parts should factor this into their material cost analysis.
Halogen content considerations. Traditional FR4 uses brominated epoxy resins (TBBPA) as the flame-retardant mechanism. In applications subject to RoHS, REACH, or end-of-life recycling regulations — particularly consumer electronics and certain export markets — halogen-free FR4 grades are required, which carry a further cost premium and may have slightly modified mechanical properties.
How to Choose Between 3240 and FR4: A Decision Framework
The choice between 3240 and FR4 is not primarily a performance question — both materials deliver comparable dielectric strength and mechanical properties. It is a compliance and application context decision. Use this framework:
- Is flame retardancy required by design code, equipment certification, or customer specification? If yes → specify FR4. No further evaluation needed.
- Is the application in an oil-immersed transformer environment with no flame rating requirement? If yes → 3240 is technically appropriate and more cost-effective.
- Does the application involve high-volume precision machining? If yes → 3240’s machinability advantage reduces tooling cost and production time.
- Is the equipment subject to high ambient humidity or condensation exposure? If yes → FR4’s lower water absorption is a meaningful long-term reliability advantage.
- Does your procurement specification reference NEMA LI-1 or IEC 60893 explicitly? If yes → FR4 aligns directly. 3240 requires cross-standard equivalence documentation.
For applications that are borderline — for example, structural components in dry-type transformers where some fire standards apply — the comparison guide on 3240 epoxy glass vs phenolic cotton laminate also provides a useful adjacent reference for understanding where epoxy laminates as a category are the appropriate material family versus phenolic alternatives. And for high-temperature applications where neither 3240 nor FR4 provides adequate thermal margin, the comparison between G10 and G11 glass-reinforced epoxy laminates should be reviewed — G11 and FR5 offer Class F (155°C) thermal ratings for applications that exceed the Class B limit of both 3240 and FR4.
Sourcing Considerations and What to Verify Before Ordering
Both 3240 and FR4 are commodity-adjacent materials with large numbers of suppliers globally. However, quality variation between manufacturers is meaningful, particularly for electrical insulation applications where property consistency across production batches directly affects equipment reliability. Before placing production-scale orders, buyers should verify:
- Material test reports (MTR): Request batch-level test data confirming dielectric strength, flexural strength, and water absorption per IEC 60893 or GB/T 1303.
- Flame test certification (FR4): Request UL 94 V-0 test certification for the specific thickness you are ordering — flame ratings are thickness-dependent and a certificate for 3mm does not automatically apply to 1mm.
- Thickness tolerance documentation: Confirm the supplier’s thickness tolerance specification. For die-cut or precision-machined parts, tight tolerance (±0.1mm or better) should be contractually specified.
- Halogen content declaration (FR4): If your application or customer requires halogen-free FR4, request a declaration of conformity confirming compliance with IEC 61249-2-21 or equivalent.
- Form factor availability: Confirm that your required form — sheet, rod, or tube — is available in the grade and thickness you need. Not all suppliers stock the full range.
SIDA’s integrated supply chain provides both 3240 and FR4 epoxy glass fiber laminates in sheet, tube, and rod form, with full material certification, export documentation, and cross-standard equivalence support. For technical consultation on material selection or to request batch test reports and samples, reach the SIDA team directly:
- Website: sidanm.com
- Email: jessie.feng@sidanm.com
- Phone / WhatsApp: +86-15958243831
Conclusion
3240 and FR4 epoxy glass fiber sheets are closely related materials with the same structural foundation but meaningfully different application profiles. 3240 excels in transformer structural insulation, precision-machined components, and cost-sensitive applications where flame retardancy is not required. FR4 is the mandatory specification wherever fire safety codes apply — PCB substrates, switchgear panels, control enclosures, and any equipment subject to UL 94 or IEC flame-rating requirements.
The most common and costly error in laminate procurement is treating these two grades as interchangeable. They are not. The right choice depends entirely on the regulatory context of your application, the environmental exposure of your equipment, and the production process you are running. Define these parameters first, then let the specification follow — rather than selecting a material and retrofitting a justification.
SIDA supplies both grades with full certification and technical support, ensuring that buyers can source the correct material, in the correct form, to the correct standard — without uncertainty at the point of incoming inspection or equipment certification.
Frequently Asked Questions
Is 3240 epoxy sheet the same as G10?
Functionally, yes. 3240 is the Chinese GB/T standard designation for an epoxy glass cloth laminate that is equivalent to NEMA G10 and IEC EPGC 201 in construction and performance. However, they are defined under different standards, and some international procurement specifications may require explicit NEMA or IEC grade documentation rather than accepting 3240 as a cross-reference. Confirm standard alignment with your customer or certification body before substituting.
Can FR4 be used in oil-immersed transformers?
Yes, FR4 is compatible with transformer oil environments and can be used for structural insulation components in oil-immersed transformers. However, for this application the flame-retardant property of FR4 provides no functional advantage, making 3240 or G10 the more cost-effective and equally valid specification for most transformer structural components.
What is the maximum operating temperature of 3240 and FR4?
Both 3240 and FR4 are rated for continuous service at approximately 130°C, placing them in IEC Class B insulation. For applications requiring Class F (155°C) or Class H (180°C) thermal ratings, G11 or FR5 grades should be specified instead.
Is halogen-free FR4 available, and when is it required?
Yes. Halogen-free FR4 (HF FR4) uses phosphorus or nitrogen-based flame-retardant systems instead of brominated epoxy. It is required in applications subject to RoHS, REACH, or specific end-of-life recycling regulations — particularly in consumer electronics and certain European export markets. Halogen-free grades carry a cost premium and should be confirmed at the specification stage rather than assumed to be equivalent to standard FR4.
Which material is easier to machine: 3240 or FR4?
3240 is generally easier to machine. The absence of flame-retardant additives — which can be abrasive — results in lower tool wear during drilling, milling, and turning operations. For high-volume production of precision-machined insulation components, this is a meaningful practical and cost advantage of 3240 over FR4.
Does SIDA supply 3240 and FR4 in rod and tube form as well as sheet?
Yes. SIDA supplies 3240 and FR4 epoxy glass fiber laminates in sheet, rod, and tube configurations, in standard thicknesses and custom dimensions. Contact jessie.feng@sidanm.com or via WhatsApp at +86-15958243831 to discuss your specific form factor and quantity requirements.
What is the difference between FR4 and FR5?
FR4 and FR5 share the same flame-retardant glass-epoxy construction, but FR5 uses a higher-performance epoxy resin system that raises the continuous thermal rating to approximately 155°C (Class F). FR5 is the correct specification when both flame retardancy and Class F thermal performance are simultaneously required — for example, in high-temperature PCB applications or flame-rated motor insulation systems. The detailed comparison of why FR5 epoxy sheet is chosen for high-temperature PCB manufacturing provides further engineering guidance on this upgrade path.
