X FR
Flame-retardant grade
ASTM D709 Grade X
FR = flame-retardant paper phenolic
Use the flame-retardant formulation when UL 94 V-0 approval is required for electrical enclosures, terminal boards and copper-clad base material; service temperature falls to 110 °C.
Values for the FR condition
Other X grades and fills
X is listed in 4 conditions; see the grade overview at X.
Compare all 4 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Cold-punchable paper phenolic | Choose the cold-punchable thin sheet (≤3 mm) for room-temperature piercing and blanking and as the base for single-sided FR-1/XPC copper-clad laminate; strength drops to 85 MPa and 110 °C. | — | 85 | 2.5 | 86 Shore D |
FRThis page Flame-retardant paper phenolic | Use the flame-retardant formulation when UL 94 V-0 approval is required for electrical enclosures, terminal boards and copper-clad base material; service temperature falls to 110 °C. | — | 85 | 1.5 | 88 Shore D |
Hot-punchable / post-forming paper phenolic | Pick the more flexible resin system when parts are punched or bent hot at about 90–130 °C in high volume; formability costs strength, at 95 MPa instead of 110 MPa. | — | 95 | 2 | 87 Shore D |
XDefault Standard paper/phenolic mechanical grade sheet | Use the general-purpose paper/phenolic mechanical sheet where moderate strength of 110 MPa, easy machining and low cost matter for low-voltage insulation and structural parts. | — | 110 | 1.5 | 88 Shore D |
What is X FR?
X FR is X in the FR grade — use the flame-retardant formulation when UL 94 V-0 approval is required for electrical enclosures, terminal boards and copper-clad base material; service temperature falls to 110 °C. X FR has a tensile strength of 85 MPa (12.3 ksi), weaker than 75% of composite grades. Elongation at break is 1.5% and the elastic modulus is 8.5 GPa (1.23 Msi). X FR has a density of 1.35 g/cm³ (0.0488 lb/in³), lighter than 75% of composite grades. Its glass-transition temperature is 150°C (302 °F). X is the default condition FabDigit quotes; FR is available on request or by drawing note.
Advantages
- Low embodied carbon — 3.5 kg CO₂/kg, better than 93% of composite grades
- Easy to machine — 70/100, better than 77% of composite grades
- Lightweight — 1.35 g/cm³ (0.0488 lb/in³), better than 75% of composite grades
Limitations
- Needs corrosion protection — 50/100, worse than 92% of composite grades
- Low fracture toughness — 1.9 MPa·√m (1.73 ksi·√in), worse than 88% of composite grades
- Absorbs moisture — dry before molding — 2%, worse than 88% of composite grades
- Limited service temperature — 110°C (230 °F), worse than 87% of composite grades
- Degrades in UV without stabilisers — 25/100, worse than 86% of composite grades
X FR properties
Typical room-temperature values for X FR; 21 are specific to this condition. Other listed values are X reference data and may not represent this condition. Bars are the position among composite grades.
Physical4
X FR has a density of 1.35 g/cm³ (0.0488 lb/in³), lighter than 75% of composite grades. Its glass-transition temperature is 150°C (302 °F).
Mechanical13
X FR has a tensile strength of 85 MPa (12.3 ksi), weaker than 75% of composite grades. Elongation at break is 1.5% and the elastic modulus is 8.5 GPa (1.23 Msi).
Thermal9
X FR is rated for continuous service to 110°C (230 °F). It conducts heat at 0.26 W/m·K (0.15 BTU/hr·ft·°F), worse than 71% of composite grades. Thermal expansion is 25 µm/m·K (13.9 µin/in·°F).
Electrical7
X FR is an electrical insulator with a dielectric strength of 14 kV/mm (355.6 V/mil) and a resistivity of 1×10⁹ Ω·m.
Chemical & Environmental3
Corrosion resistance is fair (50/100), worse than 92% of composite grades. UV resistance is poor.
Sustainability2
Producing a kilogram of X FR takes about 75 MJ of energy and emits 3.5 kg of CO₂ — less than 91% of composite grades.
Manufacturability2
X FR's machinability is very good (70/100, better than 77% of composite grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X FR
Is X easy to machine?
Cut with carbide or PCD tooling at high speed and light feed; the dust is abrasive and irritates the airway, so extraction is mandatory. Back up the exit side when drilling to prevent delamination.
Can X be welded?
Thermoset laminate — it cannot be welded or heat-fused; join with bolts, rivets or epoxy adhesive.
Can X be formed, bent or molded?
Standard Grade X is a cold-machined flat product only. Where blanking is required, specify XPC for room-temperature punching or XP for punching and post-forming after heating to 80–130 °C.
What surface finishes work on X?
Sands, chamfers, silk-screens and accepts epoxy paint. It cannot be plated; seal the edges with varnish in warm, humid service to reduce water absorption.
X 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 |
|---|---|---|
| phenol-formaldehyde resinresole/novolac phenolic binder | 35 – 50 | 42 |
| flame retardant / filleronly in FR variants | 0 – 10 | 0 |
| cellulose kraft paperreinforcement web | ≥ 50 (balance) | — |
X FR — frequently asked
What is X FR used for?
X FR is typically used for general insulation boards, low-cost mechanical spacers and electrical panel backing. In short: cheapest paper phenolic grade; general-purpose insulating board; base grade below XX.
What is the tensile strength of X FR?
X FR has a typical tensile strength of 85 MPa (12.3 ksi) — weaker than 75% of composite grades. Strength varies by condition: see the 4 listed tempers.
Is X FR easy to machine?
Yes — machinability is rated very good (70/100, better than 77% of composite grades). Cut with carbide or PCD tooling at high speed and light feed; the dust is abrasive and irritates the airway, so extraction is mandatory. Back up the exit side when drilling to prevent delamination.
Can X FR be welded?
Thermoset laminate — it cannot be welded or heat-fused; join with bolts, rivets or epoxy adhesive.
What surface finishes work on X FR?
Sands, chamfers, silk-screens and accepts epoxy paint. It cannot be plated; seal the edges with varnish in warm, humid service to reduce water absorption.
Can X FR be formed, bent or molded?
Standard Grade X is a cold-machined flat product only. Where blanking is required, specify XPC for room-temperature punching or XP for punching and post-forming after heating to 80–130 °C.
What is the maximum service temperature of X FR?
X FR is rated for continuous use to about 110°C (230 °F), and briefly to 150°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)
- Engineered Materials Handbook Vol. 2: Engineering Plastics — ASM International (1988)
- Phenolic paper laminate (X/XP/XPC) technical data — Norplex-Micarta / Professional Plastics (2023)
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.