G7 Laminate Grades — NEMA G7 & MIL-I-24768/17

The NEMA G7 grade designation identifies a woven glass fabric laminate bonded with silicone resin, defined within NEMA LI-1 (Industrial Laminating Thermosetting Products). The parallel military specification MIL-I-24768/17 covers the same material family under the type designation "GS" (Glass-Silicone), adding lot-testing requirements, traceability, and a Certificate of Conformance that NEMA commercial stock does not provide. Understanding which grade is required — and what each requires of the supplier — is essential before issuing a purchase order.

At a glance:

• NEMA G7: commercial grade, NEMA LI-1 compliance, no lot traceability required
• MIL-I-24768/17 Type GS: mil-spec grade, lot testing, CoC, and MTR required
• Single commercial grade — no sub-grades within G7 (unlike FR4's many variants)
• No flame-retardant sub-grade (G7 does not carry UL 94 V-0 under any designation)
• Color: natural (cream/tan) only — no pigmented mil-spec grades

NEMA LI-1 Grade G7: Commercial Designation

NEMA LI-1 is the governing commercial standard for laminated thermosetting materials in the United States. Within LI-1, Grade G7 is defined by:

• Reinforcement: Woven glass fabric (E-glass)
• Resin: Silicone (organopolysiloxane)
• Construction: Multiple plies, consolidated under heat and pressure
• Minimum property requirements: See the table below

NEMA G7 Minimum Property Table

NEMA LI-1 does not require lot-level testing. A supplier selling commercial G7 stock attests that the material was produced to G7 formulation; no individual lot test report is mandated unless contractually specified.

MIL-I-24768/17: Military Grade Designation

MIL-I-24768 is a multi-sheet military specification covering "Insulating Compound, Electrical, Laminated Thermosetting" materials. Sheet /17 within the specification covers the glass-silicone family. The type designation is GS (Glass-Silicone).

What MIL-I-24768/17 Adds Over NEMA G7

For procurement officers and engineers on defense programs, the practical implication is straightforward: if your drawing calls out MIL-I-24768/17, you must source from a supplier who can provide CoC and MTR for each lot shipped. Commercial NEMA G7 stock does not satisfy this requirement regardless of its performance characteristics.

MIL-I-24768/17 Type GS Properties

The minimum property values in MIL-I-24768/17 Type GS are equivalent to NEMA G7 minimums with the addition of:

• Fungus resistance (MIL-STD-810, Method 508): Specimen must show no fungal growth after 28-day exposure — important for aircraft and missile systems exposed to tropical environments.
• Thermal endurance: Specimens must pass post-aging dielectric and flexural property retention tests after conditioning at 200°C for 240 hours.

How G7 Grades Compare to Other NEMA Glass Laminates

G7 is one of five common NEMA glass-fabric laminate grades. Understanding where it sits in the family guides grade selection.

180 sec", "High-temp aerospace/power"], ["G9", "Melamine", "MIL-I-24768/14", "300–350°F", ">180 sec", "Radar, transformer, mid-temp"], ["G10", "Epoxy", "MIL-I-24768/27", "250–300°F", "60–120 sec", "PCBs, general insulation"], ["FR4", "Epoxy + FR", "MIL-I-24768/27", "250–300°F", "60–120 sec", "PCBs, UL 94 V-0 required"], ["G11", "Epoxy (HT)", "—", "300–340°F", "60–120 sec", "Elevated temp epoxy applications"], ]} />

G9's melamine resin provides a competitive middle tier — better temperature resistance than G10 and FR4, lower cost than G7 silicone — making it a common substitute when 350°F is the ceiling. When the temperature ceiling is above 350°F or when arc resistance above 120 seconds is needed, G7 is the only standard laminate grade that qualifies.

See the G7 vs. G9 comparison page for a detailed property-by-property analysis, and the G10 and FR4 vs. G7 page for the most common substitution question.

Grade Selection Logic

Use this decision tree when selecting between G7 and related grades:

1. Is continuous temperature above 350°F?

   • Yes → G7 required; G9 and G10 and FR4 are eliminated.
   • No → continue to next question.

2. Is arc resistance above 120 seconds required?

   • Yes → G7 or G9; not G10 and FR4.
   • No → G10 and FR4 acceptable if temperature is below 300°F.

3. Is UL 94 V-0 required by the end-product standard?

   • Yes → G7 does not carry UL 94 V-0. Use FR4 or specify an alternative.
   • No → G7 acceptable.

4. Is MIL-I-24768/17 called out on the drawing?

   • Yes → Source certified mil-spec lot with CoC and MTR.
   • No → NEMA G7 commercial stock acceptable.

5. Is cost a primary constraint and temperature below 350°F?

   • Yes → Consider G9 or G10 and FR4 — both are significantly less expensive per pound.

Sub-Grades and Variants: What Doesn't Exist in G7

Unlike G10 and FR4, which spawned dozens of commercial sub-grades (high-Tg FR4, halogen-free FR4, filled FR4, etc.), G7 has no equivalent proliferation. The reasons are commercial: G7's silicone resin and glass fabric make it inherently expensive, so the market for variants is narrow. You will not find:

• Flame-retardant G7 sub-grade — no halogenated-FR version exists commercially. The silicone chemistry does not produce a UL 94 V-0 result under standard test conditions.
• High-Tg G7 — standard G7 already has a glass transition above 250°C; a "high-Tg" variant adds no meaningful benefit.
• Filled G7 — glass-filled silicone compounds exist (e.g., for thermal management), but these are not laminate grades and are not sold as G7.
• Woven vs. non-woven — NEMA G7 specifies woven glass fabric. Non-woven glass (mat) reinforcement with silicone resin would be a different designation (not currently a standard NEMA grade).

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