Paper Phenolic Specifications — Sizes, Tolerances & Standards
Paper phenolic sheet, rod, and tube are produced to standard NEMA LI-1 dimensional tolerances and governed by a family of technical standards that specify both dimensions and minimum property requirements. This page covers standard slab sizes, thickness ranges, dimensional tolerances, rod and tube availability, governing standards (NEMA, MIL-SPEC, and ASTM), and the callout format for specifying paper phenolic on engineering drawings and purchase orders.
At a glance:
- Standard sheet size: 36×36", 36×48", 48×48" panels (custom slab sizes available)
- Thickness range: 1/32" through 2" in standard increments (up to 4" from some laminators)
- Thickness tolerance: ±7% under 1/4"; ±5% at 1/4" and above (NEMA LI-1)
- Rod diameters: 1/4" through 6" standard; larger on request
- Tube: various bore/OD combinations, typically 1/4" bore to 3" OD
- Governing standards: NEMA LI-1, ASTM D709, MIL-I-24768/2 (Type FBM, Grade XX); MIL-I-24768/6 (Type FBM, Grade XXX)
Governing Standards
NEMA LI-1
NEMA LI-1 (Industrial Laminated Thermosetting Products) is the primary governing standard for paper phenolic. It defines:
- Grade designations (XX, XXX, XXXP, XXXPC, and others in the paper-base family)
- Required minimum properties for each grade — dielectric strength, resistivity, flexural strength, compressive strength, water absorption
- Test methods (by reference to ASTM D-series standards)
- Standard sheet sizes and thickness tolerances
NEMA LI-1 is a performance specification; it does not dictate raw materials or manufacturing process. Any laminate that passes all required tests for a given grade designation qualifies for that designation. Buyers relying on grade designation alone should obtain actual test reports from the laminator.
ASTM D709
ASTM D709 (Standard Specification for Laminated Thermosetting Materials) runs parallel to NEMA LI-1 and is commonly referenced in U.S. procurement documents. ASTM D709 includes paper-base grades and cross-references most of the same test methods. Some government and military contracts specifically require ASTM D709 compliance rather than or in addition to NEMA LI-1.
MIL-I-24768
MIL-I-24768 is the military specification for insulating laminates in Department of Defense applications. Paper phenolic grades map to specific MIL-I-24768 type designations:
- MIL-I-24768/2, Type FBM: equivalent to NEMA Grade XX (paper, phenolic resin, general purpose)
- MIL-I-24768/6, Type FBM: equivalent to NEMA Grade XXX (paper, phenolic resin, low water absorption)
Military procurement requires traceability documentation — certified material test reports (CMTR) with laminator name, batch/lot number, date of manufacture, and test results to the applicable MIL type. Standard commercial NEMA-certified material may not satisfy MIL documentation requirements without additional supplier qualification.
IEC 60893
For projects governed by international standards (IEC, EN), IEC 60893-3-2 covers phenolic paper laminates. The IEC designations map approximately as follows:
- IEC Type PFCP 201 ≈ NEMA XX
- IEC Type PFCP 202 ≈ NEMA XXX
- IEC Type PFCP 203 ≈ NEMA XXXP
European procurement documents often specify IEC designations; confirm equivalence with the laminator for dual-standard compliance.
Standard Sheet Sizes
Standard 36×36" and 48×48" panels are stocked by most distributors in the common thickness range (1/16" through 1"). The 48×96" slab is available for larger panel requirements but may carry minimum order quantities and longer lead times. Custom slab sizes are available direct from primary laminators at economical quantities — typically 50 lbs minimum.
Cut-to-size sheets are available for most grades in standard thicknesses. Tolerances on cut dimensions are typically ±1/16" when saw-cut, ±0.010" when CNC-routed to final dimensions.
Standard Thickness Range
Thickness Tolerances (NEMA LI-1)
As a practical example: 1/8" (0.125") nominal sheet carries ±7% tolerance = ±0.009", so the acceptable range is 0.116" to 0.134". This is important for designs with critical stacking or fit-up tolerances. Precision-ground panels are available from specialty processors to ±0.002" on thickness; specify separately and expect 3–5× the cost of standard laminate.
Rod Specifications
Paper phenolic rod is manufactured by spiral-winding pre-impregnated paper strips around a mandrel under tension, then curing in an oven. The winding angle and mandrel diameter determine the available bore-to-wall ratios; sold rods are extruded from a solid wound structure.
Rod is supplied undersized (negative tolerance) because the external surface of a wound rod is not perfectly round and contains a slight resin-rich skin layer. Finish turning to final diameter is standard practice. Allow 0.020"–0.030" stock for finish turning after receiving.
Tube Specifications
Paper phenolic tube is available in a limited range of bore and OD combinations. Applications include coil forms, spacer tubes, and insulating sleeves.
Non-standard bore and wall combinations are available on manufacturer order with minimum quantity requirements. For precision bore applications, order tube oversize on ID and bore to final dimension; the wound structure of phenolic tube may have slight out-of-round on inner bore in standard condition.
Ordering and Drawing Callout Format
Use the following format on engineering drawings and purchase orders to specify paper phenolic without ambiguity:
Sheet:
Phenolic Laminate Sheet, NEMA LI-1 Grade XXX, 0.250" ± 6% thick, 36" × 48" panel size, Quantity: 10 sheets
Rod:
Phenolic Rod, NEMA LI-1 Grade XX, 1.000" nominal diameter (−0.015"/+0.000"), 36" length, Quantity: 20 pieces
MIL-SPEC:
Insulating Laminate, MIL-I-24768/6 (Grade FBM, NEMA XXX equivalent), 0.125" thick, 36" × 36" panel, per CMTR, Quantity: 5 sheets
For precision-ground panels, add:
Thickness tolerance: ±0.002" (precision ground; note: premium cost)
Surface Finish and Condition
Standard paper phenolic sheet is supplied with a smooth matte surface — not polished or textured. The surface is the natural resin-rich face formed against the press platens. Both faces on a standard slab are equivalent in surface quality.
Machined surfaces are slightly duller than the as-pressed surface. For applications requiring a specific surface finish (e.g., 125 µin Ra or better), specify machined and finished; the as-molded surface is typically 63–125 µin Ra depending on laminator.
One surface may be scored or marked with grade and batch identification from the laminator; this does not affect material performance and is removed during machining.
For full property data to pair with these specifications, see Paper Phenolic properties. For grade selection guidance, see Paper Phenolic grades. For comparison with G10 and FR4 specifications, see the G10 and FR4 specifications guide.
More related guides
Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:
Applications
Industries
Compare to other materials