Cotton Phenolic Sheet

Cotton phenolic sheet is a flat-panel thermoset laminate for jig plates, electrical panel boards, wear liners, and insulating structural members — stocked in NEMA grades C and CE from 1/16" to 4" thick, in 36"×48" and 48"×96" panel sizes, with cut-to-size service for production quantities.

TL;DR — Cotton Phenolic Sheet Quick Facts

Standard Sizes — Cotton Phenolic Sheet

Per NEMA LI 1 (Industrial Laminated Thermosetting Products):

Standard thickness increments: 1/16, 1/8, 3/16, 1/4, 5/16, 3/8, 1/2, 5/8, 3/4, 7/8, 1, 1¼, 1½, 1¾, 2, 2½, 3, 3½, 4 inches.

Non-standard thicknesses are machined from the next thicker standard size. For flatness better than the NEMA LI 1 bow allowance (1/4" per 48"), specify stress-relieved and ground sheet.

Properties Relevant to Sheet Form

Cotton phenolic sheet is anisotropic — properties are highest in the plane of the laminate (parallel to the cotton weave) and lower through the thickness. For panel and plate applications, the in-plane flexural and tensile values govern design.

Bow and flatness: NEMA LI 1 allows maximum bow of 1/4" per 48" for sheets 1/4" and thicker. Sheets thinner than 1/4" flex under their own weight and are not held to a flatness limit. For precision jig plates and fixture bases requiring flatness better than 0.005"/ft, specify thermally stress-relieved and ground sheet.

For the full property table including electrical, thermal, and chemical resistance data, see the Cotton Phenolic properties page.

Typical Applications — Sheet Form

Cotton phenolic sheet is a structural and insulating flat stock. Primary uses of the sheet form specifically include:

Electrical panel boards and bus bar mountings — Grade CE sheet cut and drilled for switchgear mounting plates, bus bar insulators, and terminal boards in industrial electrical enclosures. Dielectric strength exceeding 200 V/mil supports 600 V panel ratings.

Jig plates and fixture bases — Grade C sheet machined flat as drill jig bases, fixture body stock, and work-holding plates. The combination of compressive rigidity and machinability competes with cast iron and aluminum tooling plate while adding electrical isolation on CNC machines.

Wear liners and slide plates — Flat sheet bonded or fastened to chute walls, hopper liners, and conveyor slide surfaces in aggregate, mining, and materials-handling equipment. Cotton phenolic resists abrasive wear from bulk solids better than thermoplastic sheet in elevated-temperature environments.

Insulating panels and partitions — Motor control centers, switchboard backer panels, and field junction box insulating barriers where the sheet must carry structural load and isolate voltage simultaneously.

Gaskets and shims — Thin sheet (1/16" to 1/4") cut into insulating gaskets for flanged connections, shim stock for alignment, and anti-vibration pads.

Printed templates and pattern boards — Dimensionally stable panels for shop template use, layout tables, and marking guides in fabrication environments.

Machining Notes — Sheet

Sawing: Use a carbide-tipped table saw blade (60–80 tooth, triple-chip geometry) or a carbide-tipped circular saw blade. Feed rate: moderate and consistent. Do not force the cut — a slow, steady feed gives clean edges. Fine-tooth blades minimize edge delamination on thin sheet.

Routing and milling: Solid-carbide or carbide-insert tooling required. Climb milling at the final pass reduces edge fraying. Conventional milling for interior pockets. Depth of cut: up to 0.060" per pass for routing; 0.100" for rigid milling.

Drilling: Sharp carbide drill at 300–500 SFM; moderate feed rate. Use a backer board at the exit face to prevent fiber pullout. For blind holes, peck-drill to clear chips and prevent thermal buildup in the chip flutes.

Grinding (thickness control): Surface grinding with an aluminum-oxide or silicon-carbide wheel. Do not use coolant flooding — use dry grinding with high-airflow dust collection. Coolant can cause localized moisture absorption and surface swelling.

Punching and stamping: Thin sheet (1/16" to 1/4") can be punched with sharp steel tooling in ambient conditions. Warm the sheet slightly (100–130°F) to reduce edge cracking tendency on thicker gauges.

Dust control: Cotton phenolic dust is a respiratory irritant and combustible. Install local exhaust ventilation; operators use NIOSH P100 respirators. Follow OSHA 29 CFR 1910.94 ventilation requirements for grinding/routing.

See the Cotton Phenolic Machining Guide for detailed tool geometries, feeds and speeds tables, and finishing options.

Standards and Compliance

Request a Certificate of Conformance (C of C) citing NEMA LI 1 Grade C or CE on every order. For military applications, specify the full MIL-I-24768 documentation set at order entry.

More related guides

Applications

• Electrical Insulation — Phenolic & Laminate Options
• Bushings & Bearings — Material Selector

Industries

• General Industrial Plastics
• Aerospace Plastics

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Other cotton phenolic forms

• Cotton Phenolic Rod
• Cotton Phenolic Tube