Epoxy Resins and Compounds Terminology

A C D E F G H I L M S P R T V 0 O U

Abrasion Resistance

The resistance of a surface to rubbing or friction. A measure of durability as opposed to hardness.


The term “aliphatic” derives from the Greek word for oil- aleiphar. In chemistry, aliphatic is an adjective meaning of, relating to, or being comprised of an organic Chemical compound having an open-chain structure without unsaturation.


Adhesives are substances used for sticking objects or materials together, such as glue. 


In chemistry, aromatic is an adjective meaning of, relating to, or being comprised of an organic Chemical compound having conjugated unsaturations in a ring structure conforming to the 4n+2 rule for the number of carbons or other atoms in the ring.

Back To Top Coefficient of Thermal Expansion (CTE)

Thermal expansion is defined as the tendency of matter to change in volume in response to a change in temperature. Most matter expands as temperature increases, although there are rare examples of materials which contract as temperature rises. This effect only occurs within a limited temperature range and is limited in size. A material’s coefficient of thermal expansion is expressed as the degree of expansion divided by the change in temperature; this response to temperature change is expressed as its coefficient of thermal expansion:

The coefficient of thermal expansion is used:

  • in linear thermal expansion
  • in area thermal expansion
  • in volumetric thermal expansion

These characteristics are closely related. The volumetric thermal expansion coefficient can be measured for all substances of condensed matter (liquids and solid state). The linear thermal expansion can only be measured in the solid state and is common in engineering applications.

Epic uses test method ASTM E831.

Compressive Strength

Compressive strength is the capacity of a material to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Rigid epoxies and urethanes exhibit high compressive strengths typically with values exceeding 6000psi. Flexible materials generally do not have compressive strengths as they tend to reversibly deform rather than break.

Epic uses test method ASTM D695.


A chemical is any substance that has a defined atomic composition. Typically referring to a compound or substance in its purest form. 


A composite is something made up of several distinct parts or elements. 


A compound (chemical) is something that is composed of 2 or more separate elements in such a way that the atoms of the different elements are held together by chemical bonds. 


Conductive is an adjective meaning to allow heat or electricity to travel through. The more conductive a material is, the easier it is for heat or electricity to move through it. 

Back To Top Dielectric Constant

A dielectric constant is an essential piece of information when designing capacitors, and in other circumstances where a material might be expected to introduce capacitance into a circuit. If a material with a high dielectric constant (ie an Epoxy or Urethane potting material) is placed in an electric field, the magnitude of that field will be measurably reduced within the volume of the dielectric. This fact is commonly used to increase the capacitance of a particular capacitor design.

Epic uses test method ASTM D150.

Dielectric Strength

In physics, the term dielectric strength has the following meanings:

  • Of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down, i.e., without experiencing failure of its insulating properties.
  • For a given configuration of dielectric material and electrodes, the minimum electric field that produces breakdown.

The theoretical dielectric strength of a material is an intrinsic property of the bulk material and is dependent on the configuration of the material or the electrodes with which the field is applied. At breakdown, the electric field frees bound electrons. If the applied electric field is sufficiently high, free electrons may become accelerated to velocities that can liberate additional electrons during collisions with neutral atoms or molecules in a process called avalanche breakdown. Breakdown occurs quite abruptly (typically in nanoseconds)., resulting in the formation of an electrically conductive path and a disruptive discharge through the material. For solid materials, a breakdown event severely degrades, or even destroys, its insulating capability. Dielectric strength is reported in voltage per unit thickness of the insulator. These values are not constant for different thicknesses of the same insulator.

Epic uses test method ASTM D149.

Dissipation Factor

Electric power is lost in all dielectric materials, usually in the form of heat. The dissipation factor is expressed as the ratio of the resistive power loss to the capacitive power, and is equal to the tangent of the loss angle.

It is also referenced as the loss tangent tan delta, and approximate power factor.

In capacitors, the dissipation factor is the ratio of a capacitor's equivalent series resistance (R) to its capacitive reactance (Xc). DF is usually expressed as a percentage.

Epic uses test method ASTM D150.


Durometer is one of several measurements for the hardness of a given material—typically soft materials such as polymers, elastomers, and rubbers. The term is also used to refer to the measurement device itself. The word “durometer” is derived from the Latin word “duro”, meaning hard. In the 1920s, Albert F. Shore—founder of the Shore Instrument Company—developed a device to measure the hardness of materials. His device was not the first of its kind and was not even the first to be called a “durometer.” Nevertheless, the term “durometer” today usually refers to “Shore hardness.” Rigid materials like hard epoxy systems are measured using the Shore D Durometer. Flexible materials like urethanes similar in hardness to a tire or pencil eraser are measured with a Shore A Durometer. Very oft materials, usually urethanes, with gel like hardness are measured with a Shore OO Durometer. See also Hardness.

Epic uses test method ASTM D2240.

Back To Top Elongation

In the uniaxial tensile test commonly carried out to determine some properties of engineering materials, a small testpiece is stretched from an initial, undeformed length L0 to a current, deformed length L. Stretch ratio, also known as elongation is a measure of the deformation defined as:

\lambda = {L \over L_0}

Undeformed material then has a stretch ratio of 1.

The percent elongation is the elongation of a material expressed as the percent of the initial length.

Epic uses test method ASTM D638 or D412.


The term epoxy specifically refers to the chemical functionality provided by the chemical elements C2H4O bonded into a cycle ether arrangement.  More generally, epoxy refers to the reaction products of molecules containing multiple epoxy functionality with various chemical hardeners to from solid thermoset materials.


An exotherm is the heat generated during the chemical reaction between a resin and hardener. These exotherms are dependent of mass and surface are. If a very large mass exotherms it may result in a runaway reaction where the heat generated will cause thermal decomposition of the rein. Epoxy systems tend to exotherm more than urethanes and unfilled systems more than filled.

Electrically Conductive

An adjective meaning a material allows electricity to travel through it. 


An encapsulant is a material used for encapsulating, or enclosing something in as if in a capsule.

Back To Top Flexural Modulus

The stiffness of a structure is of principal importance in many engineering applications, so the modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is sought when deflections are undesirable, while a low modulus of elasticity is required when flexibility is needed. (see also modulus of elasticity).

Epic uses test method ASTM D790.

Flexural Strength

Flexural strength is also known as modulus of rupture, bend strength, or fracture strength. Flexural strength is measured in terms of stress, and thus is expressed in pascals (Pa) in the SI system. The value represents the highest stress experienced within the material at its moment of rupture. In a bending test, the highest stress is reached on the surface of the sample. For a rectangular sample under a load in a 3 pt bend setup:

\sigma = \frac{3FL}{2bd^2}
F is the load (force) at the fracture point
L is the length of the support span
b is width
d is thickness

For a rectangular sample under a load in a 4 pt bend setup:

\sigma = \frac{FL}{bd^2}
F is the load (force) at the fracture point
L is the length of the support (outer) span
b is width
d is thickness

Epic uses test method ASTM D790.

Fast Curing

Fast curing, in relation to resins, means fast-drying, oftentimes without the need for applied heat. 

Filtration Adhesive

Filtration adhesives are adhesives used for filter manufacturing. 

Fire Resistant

Treated as to be nonflammable. 

Fire Retardant

Having the ability or tendency to slow or stop the spread of fire. 

Back To Top Gel time

The point in time after mixing a two component material, or heating a one component material to its cure temperature, at which the material ceases to flow. The material will change from a flowable liquid to a continuous mass at this point.

Epic uses test method ASTM D3056.

Glass Transition Temperature

The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. In thermoset materials like epoxies and urethanes it is the temperature at which the cured material transitions from a rigid solid into an elastomer. Many physical and electrical properties of a material will change drastically before and after this transition.

Epic uses test method ASTM E1545 (sometimes E1356).


The term “galvanization” originally referred to various electromechanical processes named after the 18th century Italian scientist Luigi Galvani. Today, however, the term typically refers to the process of adding a thin layer of metal to an item made from steel in order to prevent rust. The term has also come to encompass the application of a protective metallic coating to metals.

Back To Top Hardness

Hardness refers to various properties of matter in the solid phase that give it high resistance to various kinds of shape change when force is applied. Hard matter is contrasted with soft matter.
One way of measuring hardness is with the use of Shore hardness gauges. These gauges impress a point into a surface under spring load. The gauge measures the resistance to the point's penetration. Harder materials are usually measured with a Shore Type "D" gauge, softer materials with a Shore Type "A" gauge, and very soft materials with a Shore Type "OO" gauge. See also “Durometer”.

Epic uses test method ASTM D2240.

Heat Distortion Temperature

The heat distortion temperature (HDT or HDTUL) is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in aspects of product design, engineering, and manufacture of products using thermoplastic components.

Hydrolytic Stability

The heat distortion temperature (HDT or HDTUL) is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in aspects of product design, engineering, and manufacture of products using thermoplastic components.

High Adhesion

High adhesion generally occurs when the contact angle is low, with adhesive forces sometimes greater than the load used to press the two surfaces together. 

High Tear Strength

High tear strength (or tear resistance) is a measure of how well a material can withstand the effects of tearing. 

High Tensile

To be very strong under tension (material). 

High Viscosity

High viscosity is when a fluid feels high resistance between adjacent layers of the fluid during relative motion. 

Back To Top Izod Impact Test

Izod impact strength is an ASTM standard method of determining impact strength. A notched sample is generally used to determine impact strength.

Back To Top Linear Shrinkage/Shrinkage

All thermoset materials shrink as they cure. The source of this shrinkage is three-fold. First, thermoset materials tend to exotherm, or heat up as they cure. The materials flow into their final shape as a liquid that is warm and then set to a solid while warm. Upon cooling back to room temperature, the solid goes through normal contraction experienced by solids as they cool. This results in a part that is smaller than the mold or part it was originally poured into.

A second source of shrinkage in thermoset materials is due to the molecular reorganization that results in the cure of the thermoset material. When a mixture of molecules reacts chemically into a single, new molecule, the distances between atoms are reduced. This decrease in molecular length results in shrinkage.

Third, in general, liquids are less dense than solids. A thermoset material begins as a lower density liquid and ends as a higher density solid. This change in density results in shrinkage.

Linear shrinkage specifically refers to the change in length of an extended volume of thermoset material on cure.

Higher exotherm materials like rigid epoxies tend to shrink more than softer ones like urethanes. Filled materials display less shrinkage than unfilled ones.

Low Adhesion

Low adhesion generally occurs when the contact angle is low, with adhesive forces sometimes less than the load used to press the two surfaces together. This causes the two surfaces to slide against each other, rather than stick.  

Low Cure Time

Low cure time means a material takes little time to cure (become harder, tougher, or more stable). 

Low Viscosity

Low viscosity is when a fluid feels low resistance between adjacent layers of the fluid during relative motion. 



Low VOC materials have reduced amounts of volatile organic compounds.

Lap Shear Strength

Lap Shear strength is the ability of an adhesive to resist forces that cause the material to adhere to substrates. Shear strength is measured in a tensile test and is measured in pounds per square inch, based on the area of the sheared edge. The shear strength of a structural adhesive is the maximum shear stress in the adhesive before failing under tensile loading. “Adhesive Failure” occurs when the material breaks free from the substrates on failure. “Cohesive Failure” occurs when the adhesive fractures before it releases from the substrate surfaces. Substrate Failure occurs when the adherents break before the adhesive fails either cohesively or adhesively.

Epic uses test method ASTM D1002.

Impact is a very important phenomenon in governing the life of a structure. In the case of aircraft, impact can take place by the bird hitting the plane while it is cruising, during takeoff and landing there is impact by the debris present on the runway. An arm held at a specific height (constant potential energy) is released. The arm hits the sample and breaks it. From the energy absorbed by the sample, its impact strength is determined. This test can normally be used to determine the notch sensitivity.

Epic uses test method ASTM D256 (notched).

Back To Top Modulus of Elasticity

An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically (i.e., non-permanently) when a force is applied to it. The elastic modulus of an object is defined as the slope of its stress-strain curve in the elastic deformation region:

\lambda \ \stackrel{\text{def}}{=}\  \frac {\text{stress}} {\text{strain}}

Where λ (lambda) is the elastic modulus; stress is the force causing the deformation divided by the area to which the force is applied; and strain is the ratio of the change caused by the stress to the original state of the object. In general, a high modulus material tends to be rigid where a low modulus one would be elastomeric like a rubber band.

Epic uses test method ASTM D638/D412 tensile, D790 flexural, D695 compressive.


Mitigating Thermal Runaway

Mitigating thermal runaway is to slow a phenomenon with lithium-ion batteries, in which the lithium-ion cell enters an uncontrollable, self-heating state. Thermal runaway can lead to the ejection of gas, shrapnel, or other particulates. Effective methods of mitigating thermal runaway include thermal insulation and reinforced heat dissipation.  

Back To Top SDS

A SDS (Safety Data Sheet) is an informational sheet which provides workers with procedures for handling and working with Epic Resins’ epoxy resins and potting compounds in a safe manner. An Epic Resins’ epoxy resin SDS provides information of physical data, storing and handling instructions, and emergency procedures to ensure maximum safety and understanding of all epoxy materials.

Shear Strength

Shear strength is the ability of a material to resist forces that can cause the internal structure of the material to slide against itself. Adhesives tend to have high shear strength. Shear strength is measured in a torsion test and is measured in pounds per square inch, based on the area of the sheared edge. The shear strength of a structural adhesive is the maximum shear stress in the adhesive before failing under torsional loading.


Synthetic materials which are polymers with a chemical structure based on chains of alternate silicon and oxygen atoms. 

Back To Top Pot Life

The length of time that a catalyzed resin system retains a viscosity low enough to be used in processing.


A synthetic rubber formed from the polymerization of monomer 1, 3-butadiene. Polybutadiene has high resistance to wear. 


Any class of natural or synthetic substances composed of large molecules called macromolecules. Macromolecules are multiples of simpler chemical units called monomers.


Polyurethane is a plastic material, which can exist in various tailored forms to be either rigid or flexible. 

Back To Top Refractive Index

The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. For example, typical glass has a refractive index of 1.5, which means that light travels at 1 / 1.5 = 0.67 times the speed in air or vacuum. Two common properties of glass and other transparent materials are directly related to their refractive index. First, light rays change direction when they cross the interface from air to the material, an effect that is used in lenses and glasses. Second, light reflects partially from surfaces that have a refractive index different from that of their surroundings.

Reaction Injection Molding

Reaction Injection Molding (RIM) is a process for forming products such as automotive panels, turbine housings, and anything requiring a high strength to weight ratio. The process is similar to injection molding, but uses thermosetting polymers which require a curing reaction within the mold. The mixture is injected into a mold under high pressure with an impinging mixer, then allowed to remain in the mold long enough to expand and cure.


Resin is a sticky, flammable organic substance that is insoluble in water. Resin is exuded by some trees and plants.


Not able to be forced out of shape without breaking; not flexible. 

Back To Top Tensile Strength

Tensile strength σUTS, or SU measures the stress required to pull something such as rope, wire, or a structural beam to the point where it breaks.

The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure. The definition of failure can vary according to material type and design methodology. This is an important concept in engineering, especially in the fields of material science, mechanical engineering and structural engineering.

Epic uses test method ASTM D638 or D412.

Thermal Conductivity

In physics, thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. It is used primarily in Fourier's Law for heat conduction.

First, we define heat conduction by the formula:       

H=\frac{\Delta Q}{\Delta t}=k\times A\times\frac{\Delta T}{x}

where \frac{\Delta Q}{\Delta t}is the rate of heat flow, k is the thermal conductivity, A is the total surface area of conducting surface, ΔT is temperature difference and x is the thickness of conducting surface separating the 2 temperatures.

Thus, rearranging the equation gives thermal conductivity,

k=\frac{\Delta Q}{\Delta t}\times\frac{1}{A}\times\frac{x}{\Delta T}

        (Note: \frac{\Delta T}{x} is the temperature gradient)

In other words, it is defined as the quantity of heat, ΔQ, transmitted during time Δt through a thickness x, in a direction normal to a surface of area A, due to a temperature difference ΔT, under steady state conditions and when the heat transfer is dependent only on the temperature gradient.

Alternately, it can be thought of as a flux of heat (energy per unit area per unit time) divided by a temperature gradient (temperature difference per unit length)

k=\frac{\Delta Q}{A\times{} \Delta t}\times\frac{x}{\Delta T}

Typical units are SI: W/(m·K) and English units: Btu·ft/(h·ft²·°F). To convert between the two, use the relation 1 Btu·ft/(h·ft²·°F) = 1.730735 W/(m·K). [Perry's Chemical Engineers' Handbook, 7th Edition, Table 1-4]

Epic uses a C-Therm test unit for measuring thermal conductivity.

Thixotropic Index

Thixotropy is the property of some non-newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite amount of time to attain equilibrium viscosity when introduced to a step change in shear rate. However, this is not a universal definition; the term is sometimes applied to pseudoplastic fluids without a viscosity/time component. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.

Thixotropic Index: obtain Brookfield viscosities using the same spindle at two different rotational speeds, usually a tenfold difference (e.g. 1 RPM and 10 RPM). This will provide a"thixotropic index" for the particular material. The higher the difference in viscosity at the two speeds, the more thixotropic the material is and easier to pump.

Epic uses test method ASTM D2196.

Thermal Cycling

Thermal cycling is essentially a stress test where a material is cycled from very low temperatures to very high temperatures to test its resilience to thermal expansion and/or expose other structural weaknesses. 

Thermal Management

The means of monitoring and controlling the temperatures produced by devices in electrical enclosures.

Thermal Runaway Propagation

A phenomenon, especially in battery packs, where a single battery cell entering thermal runaway (releasing large quantities of heat) heats up neighboring cells, causing those neighboring cells to also enter thermal runaway, starting a chain reaction of overheating. 

Thermal Shock

The rapid cooling or heating of an object (typically at a defined rate of 10°C/min. via the immediate transfer from one temperature to another. 

Back To Top Viscosity

Viscosity is a measure of the resistance of a fluid to being deformed by either shear stress or extensional stress. It is commonly perceived as "thickness", or resistance to flow. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a lower viscosity, while molasses is "thick" having a higher viscosity. The study of viscosity is known as rheology.

Epic uses test methods ASTM D2196 and D4287.

Volume Resistivity

Volume Resistivity is a measure of the intrinsic electrical resistance of an insulator. The measurement is the resistance in ohms of a material per unit area of the sample. It is typically reported in Ohm-cm as it is the resistance over a given area of material divided by its thickness.

Epic uses test method ASTM D257.

Back To Top 0 VOC

0 VOC means there are no "Volatile Organic Compounds" in the formulation. 

Back To Top Outgassing

The release of trapped gas or vapors previously dissolved, trapped, frozen, or absorbed in a solid. 

Back To Top UL Certified

Underwriter Laboratories (UL) certifies products, facilities, processes, and systems based on industry-wide laboratory standards. They are one of the oldest and most widely trusted safety certification companies. 


A urethane is the solid that forms when a multifunctional hydroxyl containing compound (polyol) chemically reacts with a multifunctional isocyanate containing compound. The resulting solid would be a urethane or polyurethane.

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