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Composite Panels

Abrasive Material
The mineral substance coating on a sanding belt that removes material from the board.
Material introduced into a panel during the manufacturing process which imparts a particular property. Additives include preservatives, water repellents, and fire retardant, but not binders.
A substance (glue) capable of bonding material together via surface attachment - such as a laminate to a panel.
ANSI A208.2-1994
The American National Standards Institute standard which sets forth requirements and test methods for dimensional tolerances, physical and mechanical properties and formaldehyde emissions for medium density fiberboard (MDF). Methods of identifying products conforming to the standard are specified. Property requirements are described in metric and imperial units. A summary of this standard is available in the Composite Panel Association’s “Buyers & Specifiers Guide” which may be viewed on-line at ( The complete standard is available from the Composite Panel Association, or from ANSI at (
Test methods published by the American Society for Testing Materials ( which may be used by MDF mills for quality control purposes.
A non-decorative laminate used on the back of composite panels to protect them from changes in humidity. Backers are often used to balance laminated panel construction with the objective of preventing warping or cupping.
Balanced Construction
A composite panel which is laminated in a fashion (usually two-sided) that resists warping when subjected to uniformly distributed changes in humidity.
The substance (generally resin) that bonds the fiber together in composite panels.
The application of binder and additives to fiber in the manufacturing of composite panels.
A localized delamination caused by steam pressure build-up during a hot pressing process. This can result from excessive moisture, adhesive (glue) spread, and/or press temperatures.
Borer Holes
Voids made by wood-boring insects, such as grubs or worms.
The deviation from flatness along the length of the panel.
Broken Grain
A (leafing, shelling, grain separation) separation on veneer surface between annual rings.
Butt Joint
A straight joint in which the interface is perpendicular to the panel face. An end butt joint is perpendicular to the grain.
The measurement of board thickness. Also refers to the tool used to measure thickness or diameter.
Center Gap
(See crossband gap)
Inner layers whose grain direction runs parallel to that of the outer plies. May be of parallel laminated plies.
A visible “wavy” condition across the surface width of a panel created when the panel is sanded. Chatter marks are parallel to one another, usually between 1/4” and 1/2” apart, and perpendicular to the sanding direction.
A lengthwise separation of wood fibers, usually extending across the rings of annual growth, caused chiefly by strains produced in seasoning.
Chip Load
The amount of material removed by each cutting tooth of a saw blade, router, or shaper, as it moves through the material being cut.
Defect created during cutting/machining when material is torn-away from the top or bottom panel edges.
Class I, II
Term used to identify different species group combinations of B-B concrete form panels.
Climb Cutting
A machining technique in which the cutting tool rotates in the same direction as the material being cut is traveling.
Composite Panel Association (CPA)
An association of North American producers of MDF, Particleboard, and Agrifiber panels located at 18928 Premiere Court, Gaithersburg, Maryland 20875. (
Construction (panel construction)
Term referring to detailed manner in which veneers are assembled and/or thickness of veneer used, e.g., “4-ply construction,” “3-layer construction,” “1/10 inch face and back,” etc.
Sometimes referred to as “crossband.”
Core Separation
Delamination of the core, often at the center line, caused by blows or insufficient internal bond.
Inner layers whose grain direction runs perpendicular to that of the outer plies. May be of parallel laminated plies. Sometimes referred to as core.
Crossband Gap and Center Gap
An open joint extending through or partially through a panel, which results when crossband or center veneers are not tightly butted.
A phenomenon in which the center of the panel is thicker along its length than at the two long edges.
Deviation from a straight line across the width of the panel.
Decorative Foils
Cellulose papers weighing between 40 and 140 grams per square meter in an untreated state. Impregnation with melamine thermoplastic resins can add 20 to 40 grams per meter - depending on the basis weight of the paper. Foils require an adhesive for lamination.
Defects, Open
Irregularities such as splits, open joints, knotholes, or loose knots, that interrupt the smooth continuity of the veneer.
The measurement of board/panel “sag” between supports when a load is applied - such as with shelving.
A visible separation between plies that would normally receive glue at their interface and be firmly contacted in the pressing operation. Wood characteristics, such as checking, leafing, splitting, and broken grain, are not to be construed as delamination. See corresponding definition for those terms. For purpose of reinspection, areas coinciding with open knotholes, pitch pockets, splits, and gaps and other voids or characteristics permitted in the panel grade are not considered in evaluating ply separation of Interior type panels bonded with interior or intermediate glue. In evaluating Interior panels bonded with exterior glue (Exposure 1), delamination in any glueline shall not exceed three square inches except where directly attributable to defects permitted in the grade as follows: Delamination associated with: Knots and knotholes - shall not exceed the size of the defect plus a surrounding band not wider than 3/4 inch. In evaluating Exterior type panels for ply separation, the area coinciding with the grade characteristics noted in paragraph (a) are considered, and a panel is considered delaminated if visible ply separation at a single glueline in such an area exceeds three square inches. All other forms of permissible defects - shall not exceed the size of the defect.
The weight of a panel as measured in pounds per cubic foot, or in kilograms per cubic meter.
Density Profile
Gradient density of a panel from face to face.
A concave area in the surface of the panel.
Direction of Grain
Usually refers to the linear direction of a wood grain pattern, or the direction in which a composite panel has moved through a sander.
Dubbing of the End (End Snipe)
Tapering of the edge of a panel as it enters and/or exits a sander.
Dulling Effect
A low-gloss area on a wet-coated panel usually caused by an incompatible finishing material, a soft panel surface, or excessive pre-heating of the panel prior to coating.
Edge Banding
A laminate material which provides a protective decorative surface for panel edges.
Edge Snipe (Rollover)
A narrow tapered condition along the edge of a panel that may be caused when the sander belt width exceeds the panel’s width. Snipe is difficult to spot visually, but can be measured with a caliper.
Edge Splits
Wedge-shaped openings in the inner plies caused by splitting of the veneer before pressing.
A process in which the panel surface is given a “relief” effect with a patterned pressure plate in a press.
Equilibrium Moisture Content (EMC)
The state at which the panel neither gains nor loses moisture given the relative humidity and temperature of the surrounding atmosphere.
The face of the plywood panel; the side of a panel that is of higher veneer quality on any panel whose outer plies (front and back) are of different veneer grades; either side of a panel where the grading rules draw no distinction between faces. The face ply of a panel; the outer veneer on the face of a panel.
Face Blisters
A dark densified area on the panel surface that may rupture or break upon cutting or machining.
Feed Rate
The speed at which material is cut/machined - usually measured in feet or meters per minute.
Fiber Raise (Fiber Pop)
A situation in which the face fibers of a composite panel have raised above the surrounding surface - usually caused by moisture absorption.
A high-solids finishing material used to fill small voids or pits in panel surfaces and edges.
Flame Spread
The rate at which flame spreads along the surface of a material as measured in a standard testing procedure. The rating is expressed in numbers or letters as they relate to finishing requirements or building codes. Plum Creek Super-Refined MDF2?, like all unrated MDF products, carries a “class C” rating.
The degree by which a material will compress before being penetrated by a cutting tool.
Thin decorative paper laminates with a melamine topcoat for durability.
A reactive organic compound (HCOH) used to manufacture binders.
MDF mill equipment that forms the furnish into a pressable mat.
The blended wood fiber and binders used in composite panel manufacturing.
Grade Name
Term used to identify panels having special characteristics and/or requirements as described under Section 3.6, such as Marine, Decorative, and Underlayment.
Grit Marks
Linear abrasions caused by the sanding process.
Grit Size
A reference to the coarseness of the abrasive material on a sanding surface. The lower the grit number, the coarser the abrasive material.
Term used to classify species covered by this Standard. Species covered by this Standard are classified as Groups 1, 2, 3, 4, and 5. See Table 1 for listing of species in individual groups and the reference in Section 2 for product use information.
A general term referring to hot pressed engineered wood panels made with refined wood and a lignin binder. Additives may be introduced during the manufacturing process to impart certain properties such as stiffness and hardness. The density range is roughly 55 to 75 pounds per cubic foot.
A measure of a panel’s resistance to surface indentation, or impact resistance, which is stated in pounds, and is related to panel density.
Nonactive core of a log generally distinguishable from the outer portion (sapwood) by its darker color.
Heat Transfer Foils
A panel laminating system involving the transfer of a complete coating surface from a carrier film to a substrate by means of heat and pressure.
Heavy White Pocket
May contain a great number of pockets, in dense concentrations, running together and at times appearing continuous; holes may extend through the veneer but wood between pockets appears firm. At any cross section extending across the width of the affected area, sufficient wood fiber shall be present to develop not less than 40 percent of the strength of clear veneer. Brown cubicle and similar forms of decay which have caused the wood to crumble are prohibited.
High Pressure Laminate (HPL)
Built-up sheet laminate constructed of multiple layers of kraft paper saturated with phenolic resin, a decorative layer impregnated with melamine resin, and a clear or tinted thin overlay heavily saturated with melamine resin. The layers are bonded together under heat and pressure to form a very durable surface for use in applications such as counter tops or panel edges.
Homogeneous Panel
A composite panel with similar fiber quality and/or density throughout its thickness.
Hook or Rake Angle
Degrees of angle on a cutting tool affecting the ease with which it penetrates the material being machined.
Hotmelt Adhesive
A 100% solid thermoplastic substance used in a variety of gluing and laminating processes. Unlike air-dried adhesives, hotmelts cure as they cool.
Impact Resistance
See “Hardness.”
Inner Plies
Plies other than face or back plies in a panel construction. Sub-face, sub-back, crossband and center are classed as inner plies.
Insulation Value
A measure of a material’s resistance to heat flow/transfer stated as “R Value.”
Internal Bond
Overall measure of panel integrity illustrating how durably the furnish is bonded together. “I.B.” is generally expressed in pounds per square inch and represents the force perpendicular to the panel surface required to pull a standard test sample apart.
Jointed Inner Plies
Crossband and center veneer that has had edges machine-squared to permit tightest possible layup.
The width of a saw cut.
Natural characteristic of wood that occurs where a branch base is embedded in the trunk of a tree. Generally the size of a knot is distinguishable by a difference in color of limbwood and surrounding trunkwood. Natural characteristic of wood that occurs where a branch base is embedded in the trunk of a tree. Generally the size of a knot is distinguishable by a difference in color of limbwood and surrounding trunkwood abrupt change in growth ring width between knot and bordering trunkwood diameter of circular or oval shape described by points where checks on the face of a knot that extend radially from its center to its side experience abrupt change in direction.
Voids produced by the dropping of knots from the wood in which they are originally embedded.
(n) A decorative overlay. (v) To bond layers of material together with adhesive.
A condition where the veneers are so placed that one piece overlaps the other.
A layer is a single veneer ply or two or more plies laminated with parallel grain direction. Two or more plies laminated with grain direction parallel is a “parallel laminated layer.”
Light White Pocket
Advanced beyond incipient or stain stage to point where pockets are present and plainly visible, mostly small and filled with white cellulose; generally distributed with no heavy concentrations; pockets for the most part separate and distinct; few to no holes through the veneer.
Linear Expansion / Contraction
Percent change in the length and width of a panel when exposed to a 50% to 80% change in relative humidity.
Any number of panels considered as a single group for evaluating conformance to this Standard.
Low Basis Weight Paper
Often referred to as “micropapers” or “rice papers” that may range in weight from 20 to 30 grams per square meter, and which are sometimes pre-impregnated with resin.
Low Pressure Laminate (LPL)
A pre-printed or solid-colored decorative paper saturated with melamine resin which, under heat and pressure, is bonded to a panel surface without the need for additional adhesive. The resulting durable surface is featured in a broad range of products from kitchen cabinetry to laminate flooring.
Refined fiber as it is formed and conveyed to the press.
Medium Density Fiberboard (MDF)
An engineered wood product made from mechanically refined wood fibers combined with resin, which are bonded together under heat and pressure. Its typical density range is 40 to 50 pounds per cubic foot (640 - 880 kg/m3). The durable homogeneous construction of MDF resists warping, cracking and splitting - offering unparalleled design flexibility where intricate shaping and finishing are required. Some of the more common uses of MDF include furniture, cabinetry, millwork, store fixtures and laminate flooring. As with solid wood, the nature of MDF can vary significantly between manufacturers, based on wood species and production technology.
Melamine Resin
A resin formulation used in the saturation of paper overlays which adheres to the panel substrate in hot press lamination.
Modulus of Elasticity (MOE)
The pounds per square inch measure of a panel’s resistance to deflection when loaded as a simple beam.
Modulus of Rupture (MOR)
The pounds per square inch measure of the maximum breaking strength of a board when loaded as a simple beam.
Moisture Content
The amount of water in the panel expressed as a percentage of dry weight.
Mottling Effect
An irregular appearance in an area (or entire surface) of a finished panel which may be caused by coarse or raised fiber, heavy application of coating material, improper drying of coating material, or incompatible solvents. Also known as “orange peel.”
Nominal Thickness
Full “designated” thickness. For example, 1/10 inch nominal veneer is 0.10 inch thick. Nominal 1/2 inch thick panel is 0.50 inch thick. Also, commercial size designation, subject to acceptable tolerances.
Refers to the degree with which finishing material masks the underlying substrate. For example, high opacity indicates more complete coverage.
A thin layer of paper, veneer, foil, or other laminate material.
An engineered wood product made from a combination of wood particles and fibers bonded together with a synthetic resin under heat and pressure. Particleboard is available in a variety of thicknesses, sizes and densities and is used in wide range of products where dimensional stability and strength are critical. Particleboard’s machinability and face integrity make it especially well-suited for laminating applications.
Inserts of sound wood or synthetic material in veneers or panels for replacing defects. “Boat” patches are oval-shaped with sides tapering in each direction to a point or to a small rounded end; “Router” patches have parallel sides and rounded ends. “Sled” patches are rectangular with feathered ends.
Phenol Formaldehyde
A water-resistant thermosetting resin used to bond softwood plywood, OSB, and some exterior or moisture-resistant grades of composite panels.
Pitch Pocket
A well-defined opening between rings of annual growth, usually containing, or which has contained, pitch, either solid or liquid.
Pitch Streak
A localized accumulation of resin in coniferous woods which permeates the cells forming resin soaks, patches, or streaks.
Small voids caused when fibers are torn out of the panel edge or surface during machining or sanding.
The rigid heated surface within a composite panel press that comes into contact with the panel surfaces.
Plugged Inner Plies
(Also referred to as solid inner plies.) - Refers to C Plugged crossband and centers and additional limitations, as given in 3.8.1.
Sound wood of various shapes, including among others, circular and dog-bone, for replacing defective portions of veneers. Also synthetic plugs used to fill openings and provide a smooth, level, durable surface. Plugs usually are held in veneer by friction until veneers are bonded into plywood.
A single veneer lamina in a glued plywood panel. (See also layer.)
Plywood is a flat panel built up of sheets of veneer called plies, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than, the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd numbered layers generally have the grain direction oriented parallel to the long dimension of the panel. The odd number of layers with alternating grain direction equalizes strains, reduces splitting, and minimizes dimensional change and warping of the panel.
Polyester Laminate
Decorative paper impregnated with polyester resin which is laminated to a backer for flat or contoured applications.
The permeability of the panel’s surface or core to liquid coatings and/or adhesives.
Post-formable HPL
High pressure laminate designed to be hot-formed around a radius where a curved design is preferred over a square edge.
Post-impregnated Paper
Paper treated (after it has been manufactured) with resin such as urea formaldehyde, melamine, or acrylic which allows the paper to remain flexible - even with the resin fully cured. These papers are easily topcoated and are available with a pre-applied hotmelt adhesive.
Pre-impregnated Paper
Paper treated (while it is being manufactured) with resin such as urea formaldehyde, melamine, or acrylic which allow the paper to remain flexible - even with the resin fully cured. These papers are easily printed or heat embossed, and are available with a pre-applied hotmelt adhesive.
A cold press in the MDF manufacturing process following the “former” that consolidates the fiber prior to hot pressing.
Either the premature curing of resin before hot-pressing, or a reference to incomplete sanding of a composite panel.
Heated platens in the MDF manufacturing process which consolidate the pre-pressed mat into a panel.
Primary Grit Marks
Linear scratches in the face of a panel from coarse sanding which are not removed by subsequent finish sanding.
The three-dimensional shape of a machined panel edge or face.
Pounds of force per square inch of panel surface.
Relative Humidity
A ratio comparing the amount of water vapor present in the air to the amount which saturated air would hold at the same temperature.
Any patch, plug, or shim.
Resin Spots
Hard pieces of dark or black material in the face layer of an MDF panel composed of resin and wood dust.
Rough Grain
Grain characteristics which prevent sanding to a smooth surface.
Rough Sand
A rough area of a panel that was not sanded with the finish heads.
The revolutions per minute speed of a motor or cutting tool.
An unsanded corner or edge of the panel (which is thicker than the rest of the panel) that may appear discolored.
A situation in which the panel face layer or laminate has been sanded off exposing the core.
Sander Hesitation
Concave linear “troughs” across the width of a panel caused when the panel stops under a moving sander head.
Sander Skip
A portion of the panel surface which wasn’t sanded, usually appearing as a rough concave area.
The living wood of lighter color occurring in the outer portion of a log. Sometimes referred to as “sap.”
Saturated Papers
Decorative papers generally weighing between 60 to 120 grams per square meter which are saturated with melamine or polyester resin, and partially cured at the point of its manufacture. Final curing occurs during hot press lamination.
The standardized test measure of force in pounds required to extract a screw from the face or edge of a panel.
A long, narrow repair of wood or suitable synthetic not more than 3/16 inch wide.
Shop-cutting Panel
A shop-cutting panel is one which has been rejected as not conforming to a standard grade because of deficiencies, other than adhesive bond quality, which prevents it from meeting the requirements of this Standard. Blistered panels are not considered as coming within the category of “shop-cutting” panel. Localized delamination may occur as a result of a deficiency. However, shop-cutting panels may be suitable for cut-up use where cutting eliminates the deficiency in the portion of the panel salvaged. Such a panel must be identified with a separate mark as specified in 6.2.1.
Snake Tracks
Serpentine raised marks on the face of the panel running along its length caused by buildup or skips on the sander belt.
Solvent Borne Adhesives
Solutions of polymers, volatile organic solvents, and crosslinking materials designed to obtain specific properties in the laminating process, such as a heat-resistance bond.
Span Rating
A set of numbers used in marking sheathing and combination subfloor-underlayment (single floor) grades of plywood as described in 3.8.5. Formerly called Identification Index.
Lengthwise separation of wood fibers completely through the veneer, caused chiefly by the manufacturing process or handling.
The degree to which a compressed MDF panel returns to its original uncompressed state.
Panels featuring right-angled corners or equal corner-to-corner diagonal measurements.
Starved Glueline
Insufficient adhesive spread in the lamination process.
The difference in height between adjoining panels due to thickness variation.
See “Pitch streak.”
Sub-face (Sub-back)
The ply adjacent to the exposed face (or back) of a parallel laminated outer layer.
The platform upon which adhesive, laminate and/or other finishing material is applied.
Thickness increase in a panel due to moisture absorption or wetting.
Tensile Strength
The maximum pounds per square inch of longitudinal stress a material can resist without tearing apart.
Thermally Fused Melamine
Paper saturated with melamine resin which is thermally fused to the substrate.
Thermofoiled Lamination
A finishing process in which a flexible laminate, such as vinyl film, is vacuum-formed over a three-dimensional surface in a heated press.
Thermoplastic Resins
Adhesives that cure at room temperature and soften upon exposure to heat.
Thermosetting Resins
Adhesives that cure in a hot press via chemical crosslinking to form rigid bonds that are not re-softened by subsequent exposure to heat.
Thickness variation within a panel, or between panels.
A sizing operation consisting of a light surface sanding in a sander. Sander skips to any degree are admissible.
Unbalanced Construction
Use of two different laminates or finishing materials on the front and back of a panel that respond unequally to changes in moisture, thus increasing the risk of warp.
Uniform Load
Weight distributed evenly across a shelf or panel.
Urea Formaldehyde (UF)
Interior grade thermosetting resin commonly used in the composite panel manufacturing process.
Thin sheets of wood of which plywood is made. Also referred to as “plies” in the glued panel.
Vinyl Film
A flexible polyvinyl chloride laminate used for decorative surfacing which may be either clear or solid-colored.
Thin to open areas in veneer sheets that result from outer log surface irregularities. Generally, only veneer peeled from the outer log surface will contain wane. Some wane areas may contain bark inclusions. For grading, wane is classed as an open defect.
Bending, twisting or turning of a panel due to unbalanced construction, exposure to excessive moisture, or other unfavorable conditions.
Waterborne Adhesives
Water-soluble adhesives such as urea formaldehyde and vinyl acetate commonly used in paper lamination.
Waterproof Adhesive
For purposes of this Standard, glue capable of bonding plywood in a manner to satisfy the exterior performance requirements given herein.
White Pocket
A form of decay (Fomes pini) that attacks most conifers but has never been known to develop in wood in service. In plywood manufacture, routine drying of veneer effectively removes any possibility of decay surviving. (Admissible amounts of white pocket permitted by this Standard were established through a 2-year research project at the U.S. Forest Products Laboratory.)
Wood failure (percent)
The area of wood fiber remaining at the glueline following completion of the specified shear test. Determination is by means of visual examination and expressed as a percent of the test area.
Wood Veneers
Solid wood laminate in a “flat,” “quarter,” “rift” or “rotary” cut.