Phenolic Glass Silicone Sheet

NEMA G7 silicone-glass sheet is the highest-temperature-rated flat laminate in common commercial production — a woven glass cloth reinforced with silicone resin, rated for 180°C (356°F) continuous service, IEC Class H thermal classification, and 180–240 seconds arc resistance, serving Class H motor insulation systems, high-voltage transformer structural barriers, and switchgear arc shields in the most demanding thermal environments.

TL;DR — NEMA G7 Sheet Quick Facts

Standard Sizes — NEMA G7 Sheet

Per NEMA LI 1:

Standard thickness increments: 1/16, 1/8, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1¼, 1½, 2 inches.

G7 sheet availability is narrower than G5 glass-phenolic or G10 glass-epoxy — some thicknesses and sizes may require 2–4 weeks lead time. Confirm availability at quotation for non-standard thicknesses.

Properties Relevant to Sheet Form

NEMA G7 sheet properties at ambient temperature are slightly below G5 glass-phenolic and G10 glass-epoxy in mechanical strength, but G7's thermal stability at elevated temperature and arc resistance are unmatched in the commercial laminate family:

The critical property at elevated temperature: G7 retains 70–80% of its ambient flexural strength at 150°C; G10 glass-epoxy retains only 20–30% at the same temperature. For applications where the insulating panel must carry structural load at its service temperature, G7 is fundamentally different from G10 — not just a variant.

Arc resistance superiority: 180–240 seconds arc resistance is the highest of any standard laminate grade. This makes G7 sheet the specification choice for arc barriers in high-voltage switchgear where fault current arcing duration cannot be bounded, and the insulating barrier must survive the arc without carbonizing through.

For the full datasheet, see Phenolic Glass Silicone properties.

Typical Applications — Sheet Form

G7 sheet's application set is the most thermally demanding in the laminate family:

Class H motor stator winding insulation — IEC 60034 and NEMA MG 1 Class H insulation systems (180°C rated) require all insulating materials — slot liners, phase barriers, end-winding separators, and coil cover sheets — to carry the Class H thermal rating. G7 sheet cut into motor slot liners and inter-phase barriers qualifies where G5 (Class F, 155°C) or G10 (Class B, 130°C) do not.

Power transformer structural insulating boards at elevated thermal loading — Large oil-filled power transformers operating near their nameplate limits (with hot-spot winding temperatures approaching 100–120°C by standard; higher in emergency loading) use G7 structural barrier boards and clamping plates where G5 glass-phenolic would be marginal.

High-voltage arc barrier panels in switchgear — G7 sheet as arc-interrupt barriers in metal-enclosed medium-voltage switchgear and load break switches where the arc must be contained without the barrier burning through. The 180–240 second arc resistance of G7 is the longest in any standard laminate and provides the greatest safety margin.

Aerospace high-temperature electrical panels — Aircraft nacelle electrical panels, engine bay junction boxes, and high-temperature avionics bay insulating panels where the ambient temperature in the installation zone exceeds the Class B or Class F thermal rating of standard glass-epoxy panels.

Industrial furnace and kiln electrical junction boxes — Insulating panel boards in electrical junction boxes mounted on or near industrial furnaces, kilns, and ovens where the panel ambient temperature can reach 150–180°C in normal operation.

Military electronics thermal insulating panels — G7 sheet to MIL-I-24768/7 (Type GSG-S) in military electronic equipment where thermal management requirements specify Class H insulating panels for sustained high-temperature operation.

Machining Notes — Sheet

G7 sheet machines with the same tooling requirements as G5 glass-phenolic — carbide or PCD mandatory:

Sawing: Carbide-tipped blade (60–80 tooth); diamond blade preferred for production cutting. Feed rate: moderate and consistent; the silicone-glass composite is somewhat softer than G10 glass-epoxy, so blade loading is slightly different — feed can be marginally faster but blade sharpness remains critical.

Routing and milling: Solid-carbide spiral bit, climb milling at final pass for edge quality. G7 sheet edges fray slightly more than G10 due to the lower resin-to-glass adhesion of silicone versus epoxy — a final light cleanup pass at reduced depth (0.010") minimizes edge fiber fraying.

Drilling: Sharp solid-carbide drill, 400–600 SFM, peck drilling for deep holes. Backer board required at exit face. G7 drills slightly more cleanly than G5 glass-phenolic in terms of hole wall quality, though glass fiber blow-out at the exit face is a consistent risk without a backer.

Laser cutting: G7 silicone-glass sheet can be laser-cut; silicone resin produces different combustion products than epoxy or standard phenolic — exhaust ventilation must handle silicone pyrolysis fumes. Consult material safety data sheet before laser cutting.

Dust and fiber control: HEPA exhaust ventilation; NIOSH P100 respirator; enclosed work area. Silicone resin decomposition products and glass fiber particulate are both respiratory hazards.

See Phenolic Glass Silicone Machining Guide.

Standards and Compliance

Request a Certificate of Conformance citing NEMA LI 1 Grade G7 on every order. For IEC Class H certification, request the thermal classification documentation from the manufacturer.

More related guides

Applications

• Electrical Insulation — Phenolic & Laminate Options
• Aerospace Interior Plastics

Industries

• Aerospace Plastics
• Electrical Power & Distribution
• Defense & Military Plastics

Compare materials

• G7 vs. G9 Laminate Comparison
• Phenolic Paper vs. Glass Phenolic

Other NEMA G7 forms

• Phenolic Glass Silicone Rod
• Phenolic Glass Silicone Tube