Definitions of Engineering Terms

To help our customers understand the terminology commonly used in thermoset plastic laminate industry, Accurate Plastics has provided a glossary of words used. If we can be of further assistance, please call us toll free at 1.800.431.2274 or use our online Request Information/Quote form.


Abrasion Resistance:
The ability to withstand the effects of repeated wearing, rubbing, scrapping, etc.

Latin meaning without form. Non-crystalline structure.

To prevent the formation of or remove stresses in plastics by cooling from a suitable temperature.

1) a luminous glow formed by the flow of electric current through ionized air, gas, or vapor between separated electrodes or contacts.
2) a portion of the circumference of a circle.

Arc Resistance:
1) the resistance to the flow of current offered by the voltaic arc (i.e., if the carbons of an arc lamp are 1/32 inch apart, the arc resistance will be 1-1/2 ohms).
2) the resistance of a material to the effects of an arc passing across its surface stated as a measure of the total elapsed time taken to form a conducting path (of material carbonizing by the arc flame) across the surface under prescribed conditions of applications of a high voltage, low current arc (as across an insulator).

Abrasion Resistance:
The ability to withstand the effects of repeated wearing, rubbing, scrapping, etc.

Abbreviation for American Wire Gauge, a standard system for designating wire diameter.


The material woven (such as paper, woven cotton, glass fabric or glass fiber mat, felted asbestos, aramid fibers, graphite, and nylon fabrics) in the form of sheets or rolls which can be impregnated with resin to form laminated plastics.

The organic or inorganic material which encapsulates and holds together the base in reinforced or otherwise heterogeneous composites.

Bond Strength:
The measure of the force required to separate objects or materials bonded together.

The disruptive discharge through insulation due to failure under electrostatic stress.

British Thermal Unit (B.T.U.):
The quantity of heat required to raise the temperature of one pound of water 1°F from 58.5°F to 59.5°F (its point of maximum density).


A cotton fabric weighing more than four ounces per square yard. (used as the base material for NEMA grades C, CE and some L grade laminates.

Also referred to as Centigrade, is equal to the difference between the temperature in Fahrenheit less 32 and the quantity divisible by 1.8. formula: °C = (°F-32) °8

A dispersion of "solution" of unvulcanized rubber or a plastic in a volatile solution. This meaning is peculiar to plastics and rubber industries and may not be an adhesive composition.

Coefficient of Thermal Expansion:
The unit change in dimension of a material for a unit change in temperature.

Coefficient of Friction:
Static: the ratio of the limiting friction developed to the corresponding normal pressure, if 2 surfaces move relative to each other.

1) a structure or an entity made up of distinct components.
2) a complex material, such fiberglass, in which two or more distinct, structurally complementary substances, especially glasses and polymers, combine to produce structural or functional properties not present in any individual component.
3) reinforced laminates (i.e. canvas phenolic, glass epoxy, etc.)

Compressive Strength:
Crushing a load at failure divided by the original sectional area of the specimen.

The reciprocal of volume resistivity. It is the conductance of a unit cube of any material.

A polymer formed through the inter-polymerization of two (or more) chemically different monomers with each other.

Copper Clad Laminate:
Laminates (i.e. FR4) having copper foil bonded to one or both surfaces and intended primarily for use in printed circuits.

Chemical action which causes destruction of the surface of a a material by oxidation or chemical combination. Also caused by reduction of the electrical efficiency between a metal and a contiguous substance or to the disintegrating effects of strong electrical currents or ground return currents in electrical systems. The latter is known as electrolytic corrosion.

Minute lines appearing in or near the surface of materials such as plastics, usually resulting as a response to environment. Crazing cannot be felt by running a fingernail across it (if the fingernail catches , it is a crack).

The dimensional change with time of a material under load. At room temperature it is also called cold flow.

A molecular structure resulting from the formation of solid crystals with a definite geometric pattern.

The setting-up of chemical valence links between the molecular chains of polymer molecules, leading to the formation of a 3-dimensional network of polymer chains which is infusible and insoluble. This usually reduces the thermoplasticity of the material.

To change the physical, chemical, or electrical properties of a material by chemical reaction, by the action of heat and catalysts alone or in combination, with or without pressure. Specifically to convert a low molecular weight polymer or resin to and insoluble, infusible state.


The separation of a laminate along the plane of it's layers. Also the separation of bonded insulation within the adhesive layer or at the adhesive interface.

Weight per unit volume of a given substance.

1) any insulating medium which intervenes between two conduits and permits electrostatic attraction or repulsion to take place across it. 2) a material having the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy. (see insulation for clarification)

Dielectric Constant (Permittivity or Specific Inductive Capacity):
The specific inductive capacity or a dielectric. That property of a dielectric which determines the electrostatic energy stored per unit volume for unit potential gradient.

Dielectric Strength:
The voltage which an insulating material can withstand before breakdown occurs, usually expressed as a voltage gradient (such as volts per mil).

Dimensional Stability:
Ability to retain precise shape and size.

Unusable or lost energy, as the production of heat in a circuit.

Dissipation Factor (loss tangent, tans, approx. power factor):
The tangent of the loss angle of the insulating material.


The fractional increase in length of a material stressed in tension.

Epoxy Resins:
Straight-chain thermosetting resins containing at least one 3 membered ring consisting of 2 carbon atoms and 1 oxygenation.

The method of processing plastic by forcing heat softened plastic through an opening of the desired shape of the cross-section of the finished product.


Fabric-Base Laminate:
Laminated insulating material formed by bonding woven cloth (of fiber glass, cotton, or synthetic fibers) with resin under heat and pressure.

Equals 1.8 multiplied to the sum of the temperature in Celsius and 32. formula: - °F = 1.8 x (°C + 32)

A thread or threadlike structure such as cellulose, wool, silk, or glass yarn. (See also fibre and filament.)

1) a specific form of chemically jelled fibrous materials manufactured in sheets, rods, and tubes.
2)commonly used interchangeably with fiber.

1)fiber characterized by extreme length.
2)the resistance wire through which filament current is sent in a therm ionic tube to produce the heat required for electron emission.

Filament Winding:
Resin impregnated roving or single strands of glass or other reinforcement wound in a predetermined pattern onto a suitable form or mandrel and then cured.

A type of vulcanized fibre paper treated chemically for insulating purposes where high mechanical and electrical strength and flexibility are required.

Flash Point:
The lowest temperature at which a flammable liquid will produce a combustible vapor that will burn in the presence of a flame, under certain prescribed conditions of test.

Flexural Strength:
The strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test specimen at the instant of failure.

A combination of ingredients before processing or made into a finished product. Also used as a synonym for a material, compound.


Glass Cloth:
Fabric used as insulating material base formed by weaving yarns comprising glass filaments and possessing high strength, heat resistance, and dielectric properties.

Glass Fiber:
Glass in fibrous form.


Heat Distortion Point:
The temperature in degrees C at which a standard test bar (ASTM D648) deflects 0.010 inches under a stated load of either 66 or 264 psi, when the temperature is raised at a specific rate of increase.

Heat Loss:
Power dissipated as heat.

High-Pressure Laminates:
Laminates molded and cured at pressures not lower than 600 psi (pressures of 1000 to 2500 psi are not uncommon).


Impact Resistance:
Relative susceptibility of material to fracture by physical shock.

Impact Strength:
Ability to withstand physical shock loading or work required to fracture under shock loading a specified test specimen in a specified manner.

To fill the voids and interstices of a material with a compound (this does not imply complete fill or complete coating of the surfaces by a hole free film.)

Deficient in active properties; not affecting other substances when in contact with them such as inert gases.

The band of light in the electromagnetic spectrum that lies between the visible light range and the radar range.

Material having a high resistance to the flow of electric current, to prevent leakage of current from a conductor.

Insulation Resistance:
The ratio of the applied voltage to the total current between two electrodes in contact with a specific conductor under prescribed conditions of test.


The absolute temperature scale (metric).; formula: - K = °C + 273

Kraft Paper:
Relatively heavy, high strength sulfate paper used for electrical insulating material.


(verb) to build up to desired shape or thickness.
(noun) a material composed of successive layers of material, usually bonded together under heat and pressure.

Light Transmission:
The amount of light that a plastic will allow to pass.

Loss Factor:
The product of the power factor and the dielectric constant.

Low Pressure Laminates:
Laminates molded and cured in the range of pressures from 400 psi down.


A randomly distributed felt of fibers, usually glass, used in reinforced plastics.

A transparent, flaky mineral which splits into thin sheets and has excellent insulating and heat resisting properties.

Moisture Resistance:
The ability of a material to resist absorbing ambient moisture.

The simple, unpolymerized form of a compound which is the building block of a polymer.


1) the passage or diffusion (or rate of passage) of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it.
2) the ability of a material to carry magnetism as compared to air which has a permeability of 1.

Preferred term for dielectric constant. It is that property of a dielectric material that determines how much electrostatic energy can be stored per unit of volume when unit voltage is applied.

Phenolic Resin:
As synthetic resin produced by the condensation of phenol with an aldehyde (usually formaldehyde).

High polymeric substances, including both natural and synthetic products, but excluding the rubbers, that are capable in their manufacture of flowing under heat and pressure.

Chemical agent added to plastics to make them softer and more flexible.

A compound formed by the chemical union of two or more monomer of the same kind.


Material used to reinforce, strengthen or give dimensional stability to another material.

A substance that is polymeric in structure and predominantly amorphous.

Property of a conductor that opposed the current flow produced by a given difference of potential. The ohm is the practical unit of resistance.

Rockwell Hardness:
A test for hardness (resistance to indentation) in which a hardened steel ball or diamond point is pressed into the material under test.


Shear Strength:
Ability of a material to withstand shear stress or stress at which a material fails in shear.

Specific Gravity:
The density of any material divided by that of water at a standard temperature.

Surface Resistivity:
The resistance of a material between two opposites sides of a unit square of its surface.


Tear Strength:
Force required to initiate or continue a tear in a material under specified conditions.

Tensile Strength:
The longitudinal stress required to break a prescribed specimen divided by the original cross-sectional area at the point of rupture (usually expressed in lbs. per square inch).

Thermal Conductivity:
The ability of a material to conduct heat; physical constant for quantity of heat that passes through volume of a substance in unit of time for unit difference in temperature.

Plastics capable of being repeatedly softened by increases in temperature and hardened by decreases in temperature. These changes are physical rather than chemical.

A classification of plastic resin that cures by chemical reaction when heated and, once cured, cannot be resoftened by heating.


Volume Resistivity:
Resistance between opposite faces of 1 cm cube of material, usually in ohm-cms.

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