Linen Phenolic Sheet
Linen phenolic sheet is the precision-grade flat laminate for electrical panel boards, instrument housings, and structural insulators that demand a finer surface finish and tighter dimensional consistency than cotton phenolic offers — with the full thermoset performance of NEMA LI 1 compliance.
TL;DR — Linen Phenolic Sheet Quick Facts
| Property | Value |
|---|---|
| Standard panel sizes | 36" × 48" and 48" × 96" |
| Thickness range | 1/16" through 2" (standard stock) |
| Thickness tolerance | ±10% below 1/8"; ±0.015" at 1/4"–1/2" (NEMA LI 1) |
| Color | Natural tan/cream; black available |
| Lead time | 1–3 days (standard stock); 2–5 days (cut-to-size) |
| Price tier | $$$ — premium over cotton phenolic; below glass laminate |
Standard Sizes — Linen Phenolic Sheet
Per NEMA LI 1 (Industrial Laminated Thermosetting Products):
| Thickness Range | Thickness Tolerance | Standard Panels |
|---|---|---|
| Below 1/8" | ±10% of nominal | 36"×48", 48"×96" |
| 1/8" to under 1/4" | ±0.020" | 36"×48", 48"×96" |
| 1/4" to under 1/2" | ±0.015" | 36"×48", 48"×96" |
| 1/2" to under 1" | ±0.020" | 36"×48", 48"×96" |
| 1" and above | ±0.030" | 36"×48", 48"×96" |
Standard thickness increments: 1/16, 1/8, 3/16, 1/4, 3/8, 1/2, 5/8, 3/4, 1, 1¼, 1½, 2 inches.
Linen phenolic sheet is less commonly stocked above 2" thickness than cotton phenolic; for heavy plate applications above 2", consider cotton phenolic Grade C. Maximum bow per NEMA LI 1 is 1/4" per 48" length for sheets 1/4" and thicker.
Properties Relevant to Sheet Form
Linen phenolic sheet properties exceed cotton phenolic modestly in flexural strength and surface hardness, while the finer linen fiber provides a smoother as-machined surface finish. The critical in-plane properties for panel design:
| Property | NEMA Grade L | NEMA Grade LE |
|---|---|---|
| Flexural Strength (lengthwise) | 16,000 psi (110 MPa) | 15,000 psi (103 MPa) |
| Tensile Strength (lengthwise) | 12,000 psi (83 MPa) | 11,500 psi (79 MPa) |
| Compressive Strength (flatwise) | 34,000 psi (234 MPa) | 33,000 psi (228 MPa) |
| Dielectric Strength (LE grade) | — | 250+ V/mil |
| Water Absorption (24 h, 1/16" sheet) | 0.8–1.5% | 0.8–1.5% |
| Continuous Use Temperature | 250°F (121°C) | 250°F (121°C) |
| Density | 1.37 g/cc | 1.37 g/cc |
| Surface Hardness (Rockwell M) | 105–120 | 100–115 |
Grade L is the structural precision grade. Grade LE adds electrical isolation: dielectric strength exceeds 250 V/mil (higher than cotton phenolic CE grade), making LE the preferred grade for high-voltage panel boards and precision electrical insulators.
For the full datasheet, see the Linen Phenolic properties page.
Typical Applications — Sheet Form
Linen phenolic sheet is selected where smooth surface finish, tight thickness control, or superior dielectric performance is more important than the cost differential over cotton phenolic:
High-voltage electrical panel boards — Grade LE sheet in motor control centers, switchgear mounting panels, and transformer terminal boards rated above 600 V. The higher dielectric strength of LE (250+ V/mil) supports medium-voltage equipment up to several kV with appropriate creepage and clearance distance design.
Precision instrument housings and chassis — Thin linen phenolic sheet (1/16"–1/4") machined into instrument enclosure panels, front panels, and PCB carrier plates in scientific and laboratory instruments where smooth surface finish and dimensional consistency matter for fitment.
Relay and contactor mounting plates — Precisely drilled and machined LE sheet panels for industrial relay boards and contactor mounting frames where bus bar and wiring connections require precise hole positioning to tight tolerances.
Antenna and RF circuit substrate panels — Linen phenolic sheet at 1/16"–1/8" thickness as the substrate for RF circuitry in lower-frequency (below 100 MHz) applications where the lower dissipation factor of linen phenolic versus cotton phenolic provides marginal signal improvement.
Thermal and electrical insulating gaskets — Thin sheet cut into precision insulating gaskets for flanged connections in electrical apparatus, particularly in applications where the gasket must also carry moderate structural load.
Photoengraving and panel engraving blanks — Linen phenolic sheet accepts engraving and chemical etching better than cotton phenolic due to the smoother, more uniform fiber matrix; used for instrument face plates and engraved legend panels.
Machining Notes — Sheet
Sawing: Carbide-tipped blade, 60–80 tooth, triple-chip geometry; moderate steady feed. Thinner sheets (1/16"–1/4") benefit from a backer sheet to prevent tear-out at the exit edge.
Milling and routing: Solid-carbide end mills or router bits; climb milling at final pass for edge quality. Because linen phenolic is harder than cotton phenolic (higher Rockwell M), reduce depth of cut slightly versus cotton — 0.040"–0.050" per pass for routing 1/4" sheet.
Drilling: Sharp carbide drill, 350–550 SFM. Smaller drill point angle (118°) works well; peck drill for holes deeper than 2× diameter. Use a backer board at the exit face. Linen phenolic drills with excellent hole wall quality — fiber pull-out is minimal with sharp tooling.
Tapping: Linen phenolic can be tapped directly for machine screw threads; use sharp bottoming taps for blind holes. Thread engagement at 1× diameter gives adequate pull-out strength for #4-40 through 1/4-20 screws.
Grinding (thickness): Aluminum-oxide or silicon-carbide wheel, dry grinding, high airflow. Linen phenolic grinds to a consistent finish with lower surface roughness than cotton phenolic due to the finer fiber matrix.
Dust control: Same requirements as cotton phenolic — localized exhaust ventilation, NIOSH P100 respirator, combustible dust precautions.
See the Linen Phenolic Machining Guide for complete parameters.
Standards and Compliance
| Standard | Scope |
|---|---|
| NEMA LI 1 | Industrial laminated thermosetting products — minimum properties per grade |
| MIL-I-24768/13 | Type FBG-LE — military linen phenolic, electrical grade (sheet) |
| MIL-I-24768/14 | Type FBG-L — military linen phenolic, mechanical grade (sheet) |
| ASTM D709 | Standard specification for laminated thermosetting materials |
Request a Certificate of Conformance citing the NEMA LI 1 grade on every order. Specify the full MIL-I-24768 documentation set for defense procurement before order entry.
Get a quote on NEMA Grade L or LE sheet — standard panels or cut-to-size
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