G10 Glass Epoxy Sheet

G-10 is the workhorse glass-epoxy laminate: woven fiberglass cloth saturated with epoxy resin and pressed under heat, giving a material that is strong, dimensionally stable and a genuinely good insulator in one. It meets NEMA G-10 - now ANSI/NEMA IM 60000-2021, previously NEMA LI 1-1998 - along with MIL-I-24768/2 Type GEE and ASTM D709 Type IV Grade G-10. Flexural strength is published at 66,000 psi lengthwise and 60,000 psi crosswise, falling to 60,000 lengthwise at.125 inch thickness, with tensile strength around 43,000 psi lengthwise and 39,000 crosswise and a hardness of Rockwell M98 to M99. The temperature index is 130C electrical and 140C mechanical.

Electrically it gives a dielectric constant of 4.8 and a dissipation factor of 0.020 at 1 MHz, a breakdown voltage parallel to the laminations of 46 to 49 kV, arc resistance of 130 seconds and a comparative tracking index of 200 V. Two numbers are thickness-dependent and worth checking against your part rather than reading off a chart. Dielectric strength perpendicular is published from 485 to 690 V/mil depending on the thickness tested - thin stock reads high, thick stock reads low, and the figures are not comparable across thicknesses. Water absorption runs 0.40% at.031 inch, 0.25% at.062 and 0.15% at.125, so thin sheet takes up nearly three times as much moisture by weight as thick.

The one thing to be clear about: G-10 is UL 94 HB. It is not flame retardant. If your application needs a flame rating, FR-4 is the same material with a flame retardant designed into the resin, and it is the grade to specify.

It is machined into terminal boards and barrier strips, insulating washers, spacers and standoffs, transformer and switchgear insulation, structural insulators, rotor and armature components, test fixtures, knife scales and handles, and model and RC parts. Natural stock is light green; black is pigmented through.

Machining and handling. The glass abrades tooling, so carbide is the floor and diamond-coated or PCD cutters are what hold tolerance in production; run high spindle speeds with secure workholding and design in generous internal radii, because small tools wear out fast against glass. Threaded holes are normally milled rather than tapped and external threads turned or thread-milled, since the plies can delaminate. The laminate has no hazards as shipped, but cutting it releases a fine dust, and the epoxy resin in that dust is classified as a skin and respiratory sensitiser - use local exhaust, a dust respirator, eye protection and gloves, and work to your own site's exposure limit, because published limits for glass dust differ by jurisdiction and by whether total or respirable dust is measured. It comes off as powder rather than chips, so vacuum it up rather than blowing it airborne. These are our shop notes, not a manufacturer specification.