G7 Glass Silicone Laminate Comparisons

G7 phenolic glass silicone holds the highest continuous-temperature rating among standard NEMA glass-fabric laminates — 425–485°F — which gives it a narrowly defined but important place in material selection. Engineers comparing G7 against alternatives are almost always asking one of three questions: Can I use G10 and FR4 instead at lower cost? Does G9 cover my temperature range? Is a different material class altogether a better fit? This page addresses each comparison with data and links to full versus pages where applicable.

At a glance:

• G7 vs. G10 and FR4: G7 wins above 300°F and when arc resistance >120 sec is needed; G10 and FR4 wins on cost and UL 94 V-0
• G7 vs. G9: G7 wins above 350°F; G9 is adequate at 300–350°F and costs less
• G7 vs. phenolic-glass: G7 surpasses all phenolic-glass grades on temperature and electrical performance; phenolic-glass costs less for low-end applications
• G7 is not interchangeable with polyimide laminates (different product class, higher cost)

G7 vs. G10 and FR4

G10 and FR4 is the most common glass-epoxy laminate globally. It dominates printed circuit board fabrication and general electrical insulation where temperature does not exceed 300°F. Comparing G7 to G10 and FR4 is the most common substitution question in laminate procurement.

Key Differences

180 sec", "60–120 sec"], ["Flexural Strength (RT)", "50,000 psi", "60,000 psi+"], ["Water Absorption (24-hr)", "<0.25%", "<0.10–0.20%"], ["UL 94 Rating", "Not rated V-0", "V-0 (FR4)"], ["MIL Specification", "MIL-I-24768/17", "MIL-I-24768/27"], ["Relative Cost", "High", "Low–Moderate"], ["Availability", "Moderate", "Very High"], ]} />

When to Use G10 and FR4 Instead

• Continuous temperature below 300°F
• UL 94 V-0 required by product standard
• Cost is a primary constraint and temperature allows it
• Very high dielectric strength (>400 V/mil) needed per spec

When G7 Is Required Over G10 and FR4

• Continuous temperature exceeds 300°F (G10 and FR4 begins to visibly soften under load above this point)
• Arc resistance specification exceeds 120 seconds
• MIL-I-24768/17 is called out on the drawing (G10 and FR4 mil-spec is /27 — different designation entirely)
• Thermal cycling from -65°F to +400°F with sustained dwell at elevated temperature

Full versus page: G10 and FR4 vs. G7

G7 vs. G9 (Phenolic-Glass-Melamine)

G9 uses melamine resin in place of G7's silicone resin, paired with the same woven E-glass fabric. Melamine resin is more thermally capable than epoxy but does not reach silicone's continuous-use ceiling. The G7 vs. G9 question arises when the operating temperature falls between 300°F and 425°F.

Key Differences

180 sec", ">180 sec"], ["Flexural Strength (RT)", "50,000 psi", "55,000 psi"], ["Water Absorption (24-hr)", "<0.25%", "<0.40%"], ["MIL Specification", "MIL-I-24768/17", "MIL-I-24768/14"], ["Relative Cost", "High", "Moderate"], ["Availability", "Moderate", "Moderate"], ]} />

G9 and G7 share identical arc resistance ratings (>180 seconds) and nearly identical dielectric strength (350 V/mil perpendicular). The sole differentiator is temperature: when operating conditions stay below 350°F, G9 delivers equivalent electrical performance at meaningfully lower material cost. When temperature exceeds 350°F continuously, G9 is not acceptable and G7 is the standard specification.

When to Use G9 Instead

• Temperature ceiling is 300–350°F (G9 rated, G7 over-specified and more expensive)
• Same arc resistance requirement (both >180 sec)
• Same dielectric strength (both 350 V/mil)
• Budget constraints — G9 costs 30–50% less per pound in typical commercial lots

When G7 Is Required Over G9

• Continuous temperature above 350°F — G9's melamine resin loses cohesion at this temperature
• MIL-I-24768/17 specifically called out (G9's mil-spec is /14)
• Thermal cycling regimes with extended dwell above 350°F

Full versus page: G7 vs. G9

G7 vs. Phenolic-Glass (G5, G7 Adjacent Grades)

Standard phenolic-glass laminates (grades such as GPO-1, GPO-2, GPO-3, and NEMA G5) use phenolic or polyester resins with woven or mat glass reinforcement. These materials carry lower continuous-temperature ratings (220–280°F) and lower arc resistance than G7.

Summary Comparison

For applications not exceeding 300°F where arc resistance is critical but cost is a constraint, GPO-3 (a polyester-glass-mat laminate with UL 94 V-0) is a lower-cost alternative with equivalent arc resistance. GPO-3 does not carry a mil-spec designation and is not acceptable on defense programs. G5 (phenolic resin, glass fabric) is a legacy grade with lower arc resistance than G7 and a lower temperature ceiling.

G7 vs. Polyimide Laminates

Polyimide-glass laminates (e.g., NEMA GI/GI-F, common in PCB substrates like Rogers 4350 or Nelco N4000) are a separate product class. Compared to G7:

• Polyimide laminates offer superior Tg (>250°C in some grades) and better dimensional stability at temperature
• They command 5–10× the cost of G7 per pound
• They are available in very thin laminate thicknesses for PCB use, not in thick structural formats like G7 sheet up to 4 in.
• G7 is preferred for structural insulation (thick section, machined parts); polyimide laminates for thin substrate/PCB applications

The two materials are not direct competitors in most procurement decisions because they serve different form-factor requirements.

Summary Decision Matrix

More related guides

Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:

Applications

• Electrical Insulation
• Aerospace Interior

Industries

• Aerospace
• Electrical Power

Compare to other materials

• FR4 Vs. G7 G7 Vs. G9