FR-6 HT-F
Grade
ASTM D709 Grade FR-6
HT-F = heat-resistant thermal class F/H polyester glass-mat board
Use where continuous service reaches 155–180 °C, e.g. motor and transformer insulation near windings.
Values for the HT-F condition
Other FR-6 grades and fills
FR-6 is listed in 4 conditions; see the grade overview at FR-6.
Compare all 4 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Hot/cold punching grade | Choose for high-volume stamped insulating washers, slot liners and PCB blanks where crack-free punching matters more than peak strength. | — | 75 | 1.4 | 100 HRM |
Enhanced flame/arc-resistant grade | Specify for arc chutes and switchgear barriers needing high ATI/CTI plus low smoke and V-0 at reduced thickness. | — | 80 | 1.1 | 108 HRM |
HT-FThis page Heat-resistant thermal class F/H polyester glass-mat board | Use where continuous service reaches 155–180 °C, e.g. motor and transformer insulation near windings. | — | 88 | 1.1 | 108 HRM |
GPO-3 / UPGM 203 | The IEC/NEMA industrial equivalent, supplied in thick sheet and rod for switchgear arc barriers and transformer insulation. | — | 90 | 1.2 | 108 HRM |
What is FR-6 HT-F?
FR-6 HT-F is FR-6 in the HT-F grade — use where continuous service reaches 155–180 °C, e.g. motor and transformer insulation near windings. FR-6 HT-F has a tensile strength of 88 MPa (12.8 ksi), weaker than 73% of composite grades. Elongation at break is 1.1% and the elastic modulus is 10.5 GPa (1.52 Msi). FR-6 HT-F has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 67% of composite grades. Its glass-transition temperature is 120°C (248 °F).
Limitations
- Hard to polish — 20/100, worse than 90% of composite grades
- Limited ductility — 1.1%, worse than 78% of composite grades
FR-6 HT-F properties
Typical room-temperature values for FR-6 HT-F; 17 are specific to this condition. Other listed values are FR-6 reference data and may not represent this condition. Bars are the position among composite grades.
Physical4
FR-6 HT-F has a density of 1.85 g/cm³ (0.0668 lb/in³), heavier than 67% of composite grades. Its glass-transition temperature is 120°C (248 °F).
Mechanical12
FR-6 HT-F has a tensile strength of 88 MPa (12.8 ksi), weaker than 73% of composite grades. Elongation at break is 1.1% and the elastic modulus is 10.5 GPa (1.52 Msi).
Thermal9
FR-6 HT-F is rated for continuous service to 155°C (311 °F). It conducts heat at 0.33 W/m·K (0.191 BTU/hr·ft·°F), worse than 53% of composite grades. Thermal expansion is 25 µm/m·K (13.9 µin/in·°F).
Electrical7
FR-6 HT-F is an electrical insulator with a dielectric strength of 14 kV/mm (355.6 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is good (64/100), worse than 74% of composite grades. UV resistance is fair.
Sustainability4
Producing a kilogram of FR-6 HT-F takes about 85 MJ of energy and emits 5 kg of CO₂ — less than 79% of composite grades. Typical recycled content is 0%.
Manufacturability2
FR-6 HT-F's machinability is fair (42/100, better than 58% of composite grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with FR-6 HT-F
Is FR-6 easy to machine?
Cut, drill and rout with carbide or PCD tooling at high speed / low feed; the glass mat and mineral filler wear HSS quickly and generate irritant dust requiring extraction.
Can FR-6 be welded?
Not weldable — thermoset; join by bonding with epoxy/polyurethane adhesives or by mechanical fasteners with generous washers.
Can FR-6 be formed, bent or molded?
Supplied as fully cured flat sheet or rod; it cannot be post-formed, but thin gauges punch cleanly (warm the sheet to 40–60 °C to avoid edge crazing).
What surface finishes work on FR-6?
Edges should be deburred and sealed with varnish or epoxy to limit moisture wicking; surface takes conformal coating and screen printing, but polishing and plating are not practical.
FR-6 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| E-glass fiber matrandom chopped-strand mat reinforcement | 25 – 40 | 32 |
| mineral filler (ATH / CaCO3)ATH also contributes flame retardancy | 20 – 40 | 30 |
| flame retardant / additivesbrominated or phosphorus FR, catalysts, pigments | 2 – 10 | 6 |
| unsaturated polyester resinmatrix, styrene cross-linked | ≥ 25 (balance) | — |
FR-6 HT-F — frequently asked
What is FR-6 HT-F used for?
FR-6 HT-F is typically used for general electrical insulation, low-cost terminal boards and appliance insulation panels. In short: low-cost flame-retardant board; punchable polyester laminate; economy alternative to FR-4.
What is the tensile strength of FR-6 HT-F?
FR-6 HT-F has a typical tensile strength of 88 MPa (12.8 ksi) — weaker than 73% of composite grades. Strength varies by condition: see the 4 listed tempers.
Is FR-6 HT-F easy to machine?
Not especially — machinability is rated fair (42/100, better than 58% of composite grades). Cut, drill and rout with carbide or PCD tooling at high speed / low feed; the glass mat and mineral filler wear HSS quickly and generate irritant dust requiring extraction.
Can FR-6 HT-F be welded?
Not weldable — thermoset; join by bonding with epoxy/polyurethane adhesives or by mechanical fasteners with generous washers.
What surface finishes work on FR-6 HT-F?
Edges should be deburred and sealed with varnish or epoxy to limit moisture wicking; surface takes conformal coating and screen printing, but polishing and plating are not practical.
Can FR-6 HT-F be formed, bent or molded?
Supplied as fully cured flat sheet or rod; it cannot be post-formed, but thin gauges punch cleanly (warm the sheet to 40–60 °C to avoid edge crazing).
What is the maximum service temperature of FR-6 HT-F?
FR-6 HT-F is rated for continuous use to about 155°C (311 °F), and briefly to 200°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D709 — Standard Specification for Laminated Thermosetting Materials — ASTM International (2017)
- NEMA LI 1 — Industrial Laminated Thermosetting Products — NEMA (1998)
- IEC 60893-3-2 — Insulating materials, industrial rigid laminated sheets, type UPGM 203 — IEC (2003)
- IEC 60112 — Method for determining proof and comparative tracking indices — IEC (2020)
- GPO-3 / polyester glass-mat laminate technical datasheets — electrical laminate producers (2023)
- GPO-3/FR-6 (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.