Glossary of Terms


The change of a material with time under defined environmental conditions, leading to improvement or deterioration of properties.
Curing agent that is any of a class of ammonia derivatives. They are derived from Ammonia (NH3).
Artificial Weathering
The exposure of product to cyclic laboratory conditions involving changes in temperature, relative humidity, and ultra violet radiant energy, with or without direct water spray, in an attempt to produce changes in the material similar to those observed after continuous outdoor exposure. Note-The laboratory exposure conditions are usually intensified beyond those encountered in actual outdoor exposure in an attempt to achieve an accelerated effect.
Bond Strength
The unit load applied in tension, compression, flexure, peel, impact, cleavage, or shear, required to break an adhesive assembly with failure occurring in or near the plane of the bond. Note-The term adhesion is frequently used in place of bond strength.
Internal void, trapped air or other gas.
A substance which markedly speeds up the cure of an adhesive when added in minor quantity as compared to the amounts of the primary reactants.
A scale of temperature which features 0° and 100° as the freezing and boiling point of water respectively. To convert centigrade to Fahrenheit multiply by 1.8 and add 32, e.g., (100° x 1.8) + 32 = 212°F.
Degree of clearness in cured encapsulant.
Coefficient Of Linear Thermal Expansion
Once cured, a measure of the change in length of an epoxy system over a given temperature range. It is expressed in inches per inch per degree C.
Coefficient Of Thermal Expansion (CTE)
Change in a unit of length or volume that accompanies a unit change in temperature.
The state in which the particles of a single substance are held together by primary or secondary valence forces observed in the tendency of the substance to stick to itself.
Compressive Modulus
The ratio within the elastic limit of compressive stress to corresponding compressive strain (deformation per original length). It is expressed in pounds per square inch. ASTM D695-54.
Compressive Strength
Crushing load at the failure of a specimen divided by the original sectional area of the specimen.
Compressive Strength, Ultimate
The maximum load in pounds that can be carried per square inch of cross section of the material under test.
Reciprocal of volume resistivity. Conductance of a unit cube of any material.
Tying together large molecules and hence changing the physical properties of material. Cross-linking usually involves formation of three dimensional molecular network and is customarily associated with thermosetting resins.
To change the physical properties of an encapsulant by chemical reaction through polymerization, usually accomplished in the presence of heat and catalyst, alone or in combination.
Cure Cycle
The schedule of time periods at specified temperatures to which a reacting thermosetting EVA composition is subjected in order to reach certain specified properties.
Curing Agent
A catalytic or reactive agent which when added to resin causes polymerization.
The ratio of a substance’s mass to its volume at a given temperature and pressure. Example-water at 25°C, 1 atmosphere of pressure =1.0 gr/cm3 = 8.35 lb. per gallon.
Dielectric Constant
When electrical energy is applied in a circuit, the insulating material of the electrical charge and releases it when the current is broken. Capacitance is the ratio of charge absorbed to the potential (voltage applied). Dielectric Constance is the ratio of an insulator's capacitance to that of dry air. (1.0). A dielectric constant of 5 means an insulator will absorb 5 times more electrical energy than air.
Dielectric Strength
The voltage which an insulating material can withstand before breakdown occurs, expressed in volts per Mil.
Any change from an initial color possessed by a material, either due to environmental or internal conditions.
Dissipation Factor
The measure of electrical energy absorbed and lost in the insulating material when energy is applied in a circuit. 20-3060 has a dissipation factor of .01. This means that .01% of the energy being stored (capacitance) is lost. Dissipation factor is the ratio of the resistive component of a capacitor to the capacitive reactance of the capacitor. Also referred to as Loss Tangent.


That property of materials by virtue of which they tend to recover their original size and shape after deformation. Note-if the strain is proportional to the applied stress, the material is said to exhibit Hookean or ideal elasticity.
A material which at room temperature can be stretched repeatedly to at least twice its original length and, upon immediate release of the stress, will return with force to its approximate original length.
Elongation (%)
Ability of a material to stretch or become longer.
Refers to the enclosure of an item in a substance. Photocap® provides encapsulation to solar modules.
Ethylene Vinyl Acetate
The removal of entrained air from an epoxy system by vacuum. Also referred to as degassing.
The liberation of heat energy during a chemical reaction. Exotherm is increased in large masses.
An available or relatively inexpensive compatible material, which can be added to a more valuable substance so as to increase the amount of material in useful form. The use of extenders may involve adulteration under some conditions.
Failure, Adhesive
The failure at the bond surface between substrates and an encapsulant; the adhesive separating entirely from the substrate.
Failure, Cohesive
Failure within the encapsulant under a stress, resulting in a broken bond with all adhered surfaces still covered with encapsulant.
Failure, Substrate
The failure of the substrate material itself, upon subjecting bonded adhered surfaces to a stress.
A substance, often inert, added to a system to improve properties and/or decrease cost.
Small globular mass which has not blended completely into the surrounding material and is particularly evident in a transparent or translucent material.
Flame Retardance
The ability of an epoxy system to resist combustion or burning. Some materials tend to extinguish themselves when subjected to a flame. Such materials are classified as self-extinguishing.
Flash Point
The temperature at which the material gives off flammable vapor in sufficient quantity to ignite momentarily on the application of a flame under specified conditions.
Flexural Modulus
The ratio, within the elastic limit, of flexural stress to the corresponding strain. It is expressed in pounds per square inch.
Flexural Strength
Ability of a material to withstand failure due to bending.
Movement of the encapsulant during the curing stages before completely cured.
Capable of being melted or fused together by melting.
The initial jelly-like solid phase that develops during the transition from a liquid to a solid.
Gel Content (Tg)
Approximate midpoint of the temperature range over which a material undergoes a phase change from brittle to rubbery or vice versa.
A substance or mixture of substances added to a polymer resin to promote or control the curing reaction by taking part in it.
Heat Distortion (Deflection) Temperature
The temperature at which a material softens enough to distort under a given load. It is not usually considered to be beyond the maximum usable temperature, but is an indication of the maximum usable temperature when the material is load bearing at a given load. As the load decreases, the maximum usable temperature will increase.
Humidity (Absolute)
The amount of moisture present in the atmosphere expressed in grams per cubic meter.
Humidity (Relative)
The ratio of the amount of moisture contained in the atmosphere to the amount of moisture that can be carried in the atmosphere at a given temperature. Relative humidity is expressed in percent, e.g., 75% R.H. at a given temperature means that the air is 75% saturated with moisture.


To fill the voids and spaces of an electrical unit with a compound. (This does not imply complete fill or complete coating of the surfaces by a hole free film).
Izod Impact Strength
A measure of the brittleness of a material. Brittle materials will have low izod impact values (.15 for example). Tough materials will have high izod impact strengths (.60 for example).
Any ingredient added to a plastic formulation that changes its properties.
Moisture Resistance
Having some resistance to high humidity. A moisture resistant polymer will not be easily affected by moisture and will not easily change its chemical and physical properties due to moisture. Should not be confused with "water proof."
OHM Unit
Unit of electrical resistance. Resistance of a circuit in which a potential difference of one volt produces a current of one ampere.
Any material is opaque if no light can be transmitted through it.
Operating Or Service Temperature
The temperature at which a plastic system can operate continuously without degradation of its properties.
Uneven surface somewhat resembling an orange peel.
Polyester EVA - Bi Laminate used in thin film modules.
The fine solid particle, usually inorganic, used in the preparation of colored products, and substantially insoluble in the vehicle. In contrast, a dye is soluble.
Small regular or irregular crater in a surface, usually with its width approximately of the same order of magnitude as its depth.
Pot Life
The length of working time of a two component reactive system from the time of the addition of the curing agent in a specific mass (i.e. 100 grams). It is expressed in minutes.
Similar to encapsulating, except that steps are taken to insure complete penetration of all the voids in the object before the resin polymerizes.
Pounds per square inch; a unit measure of pressure.


The ability of a material to resist passage of electrical current either through its bulk or on a surface. The unit of volume resistivity is the ohm-cm, of surface resistivity, the ohm.
Non woven fiberglass sheet bonded to EVA as a laminate for insulative and mechanical properties on the back side of certain polycrystalline modules. Also used as front encapsulant for flexible thin film modules.
To convert an encapsulant into a fixed or hardened state by chemical or physical action through polymerization.
Shear Strength
The shear force required to break a specimen divided by its cross-sectional area; the force being applied parallel to the cross-sectional area.
Shelf Life
The period of time during which a packaged encapsulant can be stored under specific temperature conditions and remain stable for use. Sometimes called storage life.
Shore A Hardness
The reading of a material's hardness on a durometer, the scale of which is 0-100, used on elastomers and other flexible materials. Consists of a pin point depression into the material, the material being at least 100 mils thick. A Shore A reading of 80 equals a Shore D reading of 30.
Shore D Hardness
The reading of a material's hardness on a durometer similar to the Shore A durometer, the scale of which is 0-100, used on rigid and semi-rigid materials. Consists of a pin point depression into the material.
The decrease in volume, or contraction of a material by a chemical or physical change in the material.
Softening Range
The range of temperature in which a thermoplastic changes from a rigid to a soft state.
Specific Gravity
The ratio of the weight of any volume of a mass or substance to the weight of an equal volume of water at given temperature. The specific gravity of a substance times the density of water equals the density of the substance.
An applied force or pressure, as tension or shear, exerted on a body which produces a resultant strain on the material. The ability of material to withstand a stress depends on the strength of its cohesive force or molecular resistance.
A material upon the surface of which an encapsulant is applied for any purpose, such as bonding or coating.
Surface Resistivity
The resistance to a current flow along the surface of an insulator material. Measure in ohms-cm.
Surface Tension
The property of a liquid which causes the surface to pull into the smallest area for a maximum volume, hence, drops are spherical. The fact that water drops on a wax surface do not spread out due to surface tension. If a wetting agent were to be added to the water the round droplet would spread out into a film because of the lowered surface tension.
Tensile Strength
The pulling force necessary to break a given specimen divided by the cross sectional area. Units given in lbs./in² (PSI). It measures the resistance of a material to stretching without rupture.
Thermal Conductivity
A measure of how rapidly heat is conducted through a material.
Thermal Shock Resistance
The ability of a cured system to resist cracking or crazing under conditions of rapid and continuous thermal change. The 1/4 inch TC10 test is cycled over a temperature range of -40°C to +85°C, this temperature is normally used as the test condition unless otherwise stated.
Melt processable, and reprocessable, plastic material.
Describes the property of a class of polymers, that are non-meltable after processing and cure.
Time, Curing
The period of time during which an assembly or part may be subjected to heat or pressure, to cure the encapsulant.
Tedlar® Polyester EVA - Tri Laminate Backsheet for polycrystalline and some thin film modules.
Tedlar® Polyester Tedlar® - Tri Laminate Backsheet used mainly for polycrystalline modules.
STR’s proprietary process; stands for User Friendly
Volume Resistivity
The ratio of the electrical resistance through a cross section divided by the length through which the current flows. Measured in ohms-cm.
Waviness, Surface
Wave-like unevenness, or out-of-plane in a surface.
The thorough impregnation of a material by a liquid. The more viscous a fluid, and the higher its surface tension, the more difficult it is for the liquid to "wet" materials. Certain additives, for example, water softeners, reduce surface tension, or viscosity and improve wetting properties, allowing the material to flow out more.
Yield Strength
The load in pounds per square inch where the material under test begins to change dimensions and will not completely recover when the load is removed. Yield strength will normally be lower than ultimate strength. The more rigid a material is, the closer will be yield and ultimate strengths. The more resilient a material is, the greater the spread between yield and ultimate strengths.
© STR Holdings, Inc. 2021 Home Site Map Contact Us Terms of Use Privacy Policy
Website By FIREHORSE Creative LLC Concord NH