FR4 Comparisons — FR4 vs G10, G11, Cotton Phenolic & Halogen-Free

FR4 is evaluated against several alternative laminates most often: G10 (its non-flame-retardant glass-epoxy counterpart), G11 (elevated-Tg glass-epoxy), cotton phenolic laminates (lower cost, lower performance), and halogen-free FR4 variants (environmental compliance alternative). Each comparison has a distinct decision driver — primarily flame retardancy, operating temperature, CTI, cost, or environmental compliance. This page organizes the key head-to-head comparisons and links to dedicated versus pages where available.

At a glance:

• FR4 vs G10: flame retardancy (V-0 vs none) is the deciding factor; properties otherwise nearly identical
• FR4 vs G11: G11 offers higher Tg (155°C+) and V-0 rating at higher cost
• FR4 vs cotton phenolic: FR4 wins on electrical performance; phenolic wins on machinability and cost
• FR4 vs GPO-3: GPO-3 offers higher CTI (Group II) at the cost of lower dielectric strength
• Halogen-free FR4 vs standard FR4: same V-0 rating, higher Dk, no TBBPA

FR4 vs G10 — The Most Important Comparison

FR4 and G10 are the two most commonly confused laminates in electrical insulation procurement. Both are woven-glass-reinforced epoxy thermosets. The single, critical difference: FR4 carries UL94 V-0 flame retardancy; G10 does not.

For the full dedicated comparison, see G10 vs FR4.

When to use FR4 over G10: Any application governed by UL 94, NEC, IEC 60950-1/62368-1, UL 508, or similar standards requiring V-0 flame retardancy in the insulating material. This includes virtually all PCBs, most switchgear components, and any electrical enclosure sold under UL or CE certification.

When to use G10 over FR4: Applications where flame retardancy is genuinely not required (some aerospace wet-lay tooling, marine outboard components, custom structural laminates) and cost reduction is a priority. Some high-frequency applications prefer G10 for marginally lower Dk variation from the absence of TBBPA. If you are comparing G10 and FR4 for a commercial electrical product, default to FR4.

FR4 vs G11

G11 is a glass-epoxy laminate with a multifunctional epoxy resin system that raises the Tg to 155°C+ versus 130–140°C for standard FR4. G11 also carries UL94 V-0 rating — it is flame-retardant by resin chemistry rather than TBBPA addition (or in some formulations, a combination).

When to use G11 over FR4: High-temperature structural insulation where the part must maintain properties above 140°C but cost does not justify polyimide or ceramic laminates. G11 is not a PCB substrate — its resin system is optimized for thermal performance rather than PCB processability. For PCBs requiring Tg > 140°C, use high-Tg FR4 (IPC-4101 /41 or /42) rather than G11.

When to use FR4 over G11: Standard operating temperature applications where the Tg of 130–140°C provides adequate margin (>20°C above maximum operating temperature). FR4 is less expensive and more widely available than G11.

FR4 vs Cotton Phenolic Laminates

Cotton phenolic (NEMA grade CE, LE, L) laminates use cotton fabric reinforcement and a phenol-formaldehyde resin matrix — a fundamentally different chemistry from glass-epoxy.

When to use FR4 over cotton phenolic: Whenever electrical performance (dielectric strength, moisture resistance) is important, or when V-0 flame rating is required. FR4 outperforms phenolic laminates in every electrical property category.

When to use cotton phenolic over FR4: Low-cost structural and electrical applications with moderate electrical requirements, where phenolic's machinability advantage and lower price matter. Cotton phenolic machines with less tool wear than FR4 and produces less abrasive dust. Phenolic gears, punch press dies, and transformer coil formers at low voltage are classic applications where phenolic cost advantage is real. See the cotton phenolic material hub for details.

FR4 vs GPO-3

GPO-3 (glass-polyester, thermosetting) is an arc-resistant glass-reinforced thermoset with UL94 V-0 rating. Its primary advantage over FR4 is its Comparative Tracking Index:

When to use GPO-3 over FR4: Applications where CTI Group II (≥ 400 V) is required by IEC 60664-1 for the rated voltage and pollution degree. This applies to medium-voltage switchgear, motor starter contactors, and arc flash barriers where tracking resistance under contamination is the primary failure mode to guard against.

When to use FR4 over GPO-3: Whenever dielectric strength, moisture resistance, and PCB substrate compatibility matter more than tracking resistance. FR4's dielectric strength of ~500 V/mil versus GPO-3's ~300 V/mil is a significant advantage for through-thickness insulation in high-voltage assemblies.

FR4 vs Halogen-Free FR4

Both achieve UL94 V-0 rating — the choice between them is environmental compliance, not flame performance.

When to choose halogen-free FR4: OEM procurement specifications mandating halogen-free per IEC 61249-2-21; EU market products where REACH SVHC communication obligations for TBBPA create supply chain documentation burden; designs prioritizing end-of-life recyclability and reduced environmental persistence.

When to choose standard FR4: Cost-sensitive applications where halogen-free premium is not justified by regulatory requirements; applications below ~1 GHz where the slightly higher Dk of halogen-free FR4 is irrelevant; standard commercial electronics not subject to halogen-free mandates.

Quick-Reference Comparison Table

More related guides

Product forms

• FR4 Sheet
• FR4 Plate

Compare to related materials

• G10 Material Hub
• Cotton Phenolic Material Hub

Frequently asked questions — FR4 FAQ