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Glossary of Terms O-Z


Octave Band: A frequency band with an upper frequency limit equal to twice the lower limit.
Offset: A change in location or direction of a main, branch or runout. It may be located in a riser or: horizontal run of piping or duct.
One-coat Cement: A mixture of various insulation fibers, fillers and binders with hydraulic-setting cement. The: material can be applied directly to fittings to match adjacent insulation thickness in one: application and smoothed to provide a hard finish.
Open Cell Foam: A material comprised predominantly of interconnecting cellular voids.
Panel: A prefabricated unit of insulation and lagging.
Patching: Repair or restoration of damaged existing insulation. See Reinsulate.
Perlite: Insulation composed of natural perlite ore expanded to form a cellular structure.
Perm: The unit measure of vapor transmission consisting of one grain of water through one square foot: of a membrane in an hour at 1-inch mercury vapor pressure difference.
PERMEABILITY: The property of a substance which permits passage of water vapor and is equal to the permeance of an inch (1) of thickness of the substance. Permeability is measured in Perm inches.
PERMEANCE (Perms): The ratio of water vapor flow to the vapor pressure difference between the two surfaces of a sheet of material (or the assembly between parallel surfaces). Permeance is measured in Perms.
Personnel Protection: Insulation installed for the purpose of protecting personnel from hot surfaces.
pH: A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions,: increasing with increasing alkalinity and decreasing with increasing acidity (potential of: hydrogen).
Phenolic Foam: A foamed insulation made from resins of phenols condensed with aldehydes.
Pin Weld: Attachment of insulation anchor pins to ductwork or equipment usually by capacitor discharge: welding.
Pinhole: Very small hole through a mastic or coating.
Pipe Insulation: Insulation in a form suitable for application to cylindrical surfaces.
Pipe: A circular conduit for the conveyance of liquids or semisolids.
Plenums: A compartment or chamber to which one or more ducts are connected, that forms a part of the air: distribution system, and that is not used for occupancy or storage. A plenum is often formed in: part or in total by portions of the building.
Pointing: Applying or shaping cements or mastic with a small pointed trowel.
Polyethylene: A closed-cell, thermoplastic material used for insulation.
Polyimide: See cellular polyimide.
Polyisocyanurate: A closed-cell, thermoset, plastic foam formed by combining isocyanurate, polyol, surfactants,: catalysts and blowing agents.
Polymer: A long chain molecule resulting from the chemical attachment of short molecules (monomers) of: the same product. For example, when ethylene (a gas) is polymerized, the synthetic resin: polyethylene is produced.
POLYOL: An organic compound having more than one hydroxyl (-OH) group per molecule. In the cellular plastics industry, the term includes monomeric and polymeric compounds containing alcoholic hydroxyl groups such as polyethers, glycols, glycerol, and polyesters, used as reactants in polyurethane foam.
Polyolefin: A closed-cell thermoplastic material used for insulation.
POLYSTYRENE: A resin made by polymerization of styrene as the sole monomer.
POLYURETHANE: Polymeric substance containing many urethane linkages. Abbreviated as PUR or PIR, depending on whether there is a greater proportion of polyol or isocyanate. [Rigid foam polyurethanes with higher isocyanate indexes are referred to as PIR, or polyisocyanurate foam]. Polyurethanes actually include a very large family of polymers with widely ranging properties and uses, all based on the reaction product of an organic diisocyanate with compounds containing a hydroxyl group, and having the 'RNHCOOR’- group in their chains. The types and properties of polyurethanes are so varied that they have been dubbed the "erector set" of the plastics industry. They may be thermosetting or thermoplastic, rigid and hard or flexible and soft, solid or cellular; and the properties of any of these types may be varied within wide limits to suit the desired application. See Polyisocyanurate.
Polyvinyl Chloride (PVC): A polymerized vinyl compound using chloride.
Polyvinyl Fluoride (PVF): A polymerized vinyl compound using fluoride.
Pressure Sensitive Tape: A tape with adhesive pre-applied.
Pumped Condensate (Discharge): Condensate in liquid state from condensate receivers to feed water heaters, deaerators or boilers.
Puncture Resistance: That property of a material that enables it to resist punctures or perforations under blows or: pressure from sharp objects.
Punking: An exothermic reaction that occurs inside insulation material, on a hot surface, and usually is the: result of the combustion of gasses resulting from chemically decomposed binder or resin.
Radiance: The rate of radiant emission per unit solid angle and per unit projected area of a source in a: stated angular direction from the surface (usually the normal).
Radiant Flux Density: The rate of radiant energy emitted from unit area of a surface in all radial directions of the: overspreading hemisphere.
RADIANT HEAT: Heat radiating from a heated body, as distinguished from that transmitted by an intervening body.
Radiation: The passage of heat from one object to another without warming the space between.
Reflectance: The fraction of the incident radiation upon a surface that is reflected from the surface.
Reflective Insulation: Insulation depending for its performance upon reduction of radiant heat transfer across air spaces: by use of one or more surfaces of high reflectance and low emittance.
Refractory Insulation: Insulation for extremely high temperatures, applications usually above 1500°F.
Refractory Materials: Materials, usually fibers, that do not significantly deform or change chemically at very high: temperatures. Manufactured in blanket, block, brick or cement form.
Reinforcing Cloth or Fabric: A woven cloth or fabric of glass or resilient fibers used as reinforcement to a mastic.
Reinsulate: To repair insulation to its former condition. (If insulation is to be removed and replaced, it should: be so stated.)
Relative Humidity: One of the following ratios (a) the mole fraction of water vapor in a given moist air sample to the: mole fraction in the air sample saturated at the same temperature and pressure; (b) the vapor: pressure in a given moist air sample to the vapor pressure in the air sample saturated at the same: temperature and pressure and (c) the humidity ratio in a given moist air sample to the humidity: ratio in the air sample saturated at the same temperature and pressure. There are no units.
Removable and Reusable Covers: Insulation materials or pads, enclosed in a fabric or metal (mesh, or sheet), designed to be readily: removed and reinstalled.
Resiliency: The property of a material that enables it to recover its original shape and thickness after: compression.
Resistance to Acids, Caustics, and Solvents: The ability of a material to resist decomposition by various acids, caustics and solvents to which: it may be subjected.
Resistance to Air Erosion: The ability of an insulation material to resist erosion by air currents over its surface.
RESISTANCE to fungal or bacterial growth: Is necessary in food or cosmetic process areas.
RESISTANCE to ultraviolet light: Significant if application is outdoors.
Resistance, Abrasion: The ability to withstand scuffing, scratching, rubbing or wind-scouring.
Resistance, Freeze-Thaw: Resistance to cycles of freezing and thawing that could affect application, appearance or: performance.
Resistance, Impact (Toughness): Ability to withstand mechanical blows or shock without damage seriously affecting the: effectiveness of the material or system.
Resistance, Thermal, (R-value): A measure of the ability to retard heat flow rather than the ability to transmit heat. R-value is the: numerical reciprocal of “U” or “C,” thus R = 1/U or 1/C. Thermal resistance R-value is used in: combination with numerals to designate thermal resistance values: R-11 equals 11 resistance: units. The higher the “R,” the higher the insulating value. The I-P units are °F – ft2 – hr / Btu; the: SI units are °C – m2 / W.
Resistivity, Thermal, r: The quantity determined by the temperature difference, at steady state, between two defined: parallel surfaces of a homogeneous material of unit thickness, that induces a unit heat flow rate: through a unit area. (r in SI units: m K/W.) (r in inch-pound units: h ft F/Btu or, h ft ² F/Btu in.): Retrofit: The application of additional insulation over existing insulation, new insulation after old: insulation has been removed, or new insulation over existing, previously uninsulated surfaces.
RETROFIT: The application of additional insulation over existing insulation, new insulation after old insulation has been removed, or new insulation over existing, previously uninsulated surfaces.
Return Air Duct: A duct carrying air from a conditioned space to the mixing air duct or plenum unit.
Return Air: Air returned from conditioned spaces to an air-handling unit.
Rigid Wrap-around Insulation: Segments of insulation material that have been adhered to a facing giving rigid insulation: materials flexibility of application.
Rigidity: The property of a material that opposes any tendency for it to bend (flex) under load.
Riser: The vertical portion of a main, branch or runout.
Rock Wool (Mineral Wool): A synthetic vitreous fiber insulation made by melting predominantly igneous rock and other: inorganic materials, and then physically forming the melt into fibers. See Mineral Wool.
RUBBERIZED ASPHALITIC VAPOR RETARDER: Polymer modified bituminous jacketing.
Run-Out: Piping or duct work from or to a branch or main serving one: a) plumbing unit or fixture: connection. b) heating and/or cooling unit, coil, convector, unit heater, fin tube, equipment: connection, etc. c) HVAC diffuser or register or d) process equipment connection.
R-Value (Resistance): See Resistance, thermal.
Saddle: Rigid support for piping or equipment with allowance for insulation.
Sample: A group of items, observations, test results, or portions of material, taken from a large collection: of items, observations, test results, or quantities of material, which serves to provide information: that may be used as a basis for making a decision concerning the larger collection.
SBCCI: Southern Building Code Congress, International.
S-Clip: A device (in the shape of an “S”) for supporting insulation, bands or jacketing.
Score: To cut grooves in rigid insulation so that it may be cracked and fitted to round or irregular: surfaces.
Seal: To make water-tight or airtight.
Sealant: Sealants in insulation function primarily as water and vapor seals. They may also be used as: adhesives, and for expansion joints for metal, masonry, cellular glass, etc. They must exhibit low: shrinkage, excellent adhesion and permanent flexibility.
Sealer: A liquid coating used to prevent excessive absorption of finish coats into porous surfaces.
Securements: Any device, wire, strap or adhesive used to fasten insulation into its service position and hold it: there.
Self-Extinguishing: The property of a material that enables it to stop its own ignition after external ignition sources: are removed.
Service Temperature Limits: The temperature to which the jacket or coating may be subjected when applied over insulation. It: does not refer to the operating temperature of the equipment, vessel or pipe.
SHEAR MODULUS: Shear modulus, sometimes referred to as the modulus of rigidity, is defined as the ratio of shear stress to the shear strain. Shear modulus is usually measured in ksi (kips per square inch) or GPa (gigapascals).
Shear Strength: The ability of a material to resist cleavage.
Shelf Life: The period of time during which a material, especially packaged adhesive, coating or sealant,: can be stored under specified temperature conditions and remain suitable for use.
Shield: Metal protector to prevent crushing of insulation at pipe hangars.
Shrinkage: That property of a material that indicates its proportionate loss in dimensions or volume due to: temperature changes or aging.
SLAG WOOL: A type of inorganic, fibrous insulation manufactured from blast furnace slag.
Smoke Density: The amount of smoke given off by the burning material compared to the amount of smoke given: off by the burning of a standard material.
SMOKE DEVELOPMENT: Smoke Development is the characteristic of a material to emit smoke when exposed to flame or fire. Building codes generally require a smoke development rating of 50 or less, as measured per ASTM E84. Other codes require a rating of 450 or less, which meets Class 1 requirements. Smoke development can also be measured per UL723.
Soaking Heat: A test condition in which the specimen is completely immersed in an atmosphere maintained at a: controlled temperature.
Solar Resistance: The property of a material to resist decomposition by the ultraviolet rays from the sun or the: passage of radiant heat from the sun.
Solids Content: The percentage of the non-volatile matter in adhesives, coatings or sealants. It may be based on: weight or volume.
Solvent: Any substance, usually a liquid, that dissolves another substance.
Sound Absorption Coefficient (SAC): The percentage of sound energy incident on the surface of a material that is absorbed by the: material.
Sound Transmission Class (STC): A single number rating based on sound transmission loss measurements of a partition between: adjacent closed rooms.
Sound Transmission Loss (STL): The reduction in level measured in decibels as sound energy passes through a material or: composite construction.
Specific Heat: The ratio of the amount of heat required to raise a unit mass of a material 1 degree, to that: required to raise a unit mass of water 1 degree at some specified temperature.
Sprayed-on Insulation: Insulation of the fibrous or foam type that is applied to a surface by means of power spray: devices.
SSL: Self-sealing lap, as in the overlap on pipe insulation jacket.
Standing Seam: Folded configuration of jacketing to achieve watershed for the top flat surfaces of ductwork,: vessels, or tanks. Also used to provide rigidity.
Steady State (Thermal): A condition for which all relevant parameters in a region do not vary over two consecutive: steady-state time periods by more than the steady-state tolerance, and no long-term monotonic: drifts are present. Where, the steady-state time period is the time constant of the apparatusspecimen: system with additional time necessary if physical phenomena are present, such as: moisture transport, which could cause a long-term monotonic drift.
Stiffener (Duct Flange): A structural or fabricated angle iron shape, attached to the exterior surfaces of a duct or bulkhead: at specified intervals for the purpose of reinforcing the metal and to prevent vibration.
Strainer: A filter or sieve used in fluid piping to trap scale and other entrained particles.
Strength, Transverse (or Flexural): The breaking load applied normal to the neutral axis of a beam.
Stud Weld: Attachment of insulation anchors to tanks or vessels by means of drawn arc welding.
Stud: Used to hold heavy insulation and/or panels in place. Applied with arc welder, studs differ from: pins in that they are generally ¼-inch or greater in diameter.
Supply Air Duct: A duct that carries conditioned air from air supply units to room diffusers or grilles.
Support (Insulation): A mechanical device that carries the weight of insulation.
SUPPORT (Insulation): A mechanical device which carries the weight of insulation.
Surface Coefficient: The ratio of the steady-state heat exchange rate (time rate of heat flow per unit area of a: particular surface by the combined effects of radiation, conduction, and convection) between a: surface and its external surrounding (air or other fluid and other visible surfaces) to the: temperature difference between the surface and its surroundings. (See conductance, film).
Surface Temperature (TA): The surface temperature of finished insulation.
Tack: The property of an adhesive that enables it to form a measurable bond immediately after: adhesive and adherent are brought into contact under low pressure.
Tear Strength: The property of a material that enables it to resist being pulled apart by opposing forces.
Temperature Limits: The upper and lower temperatures at which a material will experience no change in its physical: properties.
Test Specimen: The portion of a test unit needed to obtain a single test determination.
Thermal Conductivity (k-Value): See Conductivity, thermal (k-value)
Thermal Capacity: The quantity of heat required to change the temperature of the body one degree. For a: homogeneous body, it is the product of mass and specific heat. For a nonhomogeneous body, it is: the sum of the products of mass and specific heat of the individual constituents. (May also be: seen as heat capacity.)
Thermal Insulation: Definition One: Insulation applicable within the general temperature range of –300 F to 1800 F. Definition Two: A material or assembly of materials used to provide resistance to heat flow.
Thermal Insulation System: Applied or installed thermal insulation complete with any accessories, vapor retarder, and facing: required.
Thermal Properties of Insulation: Usually expressed as C-value, K-value, R-value and U-value.
Throat: Inside radius of an elbow.
TOXICITY: Must be considered in food processing plants and potential fire hazard areas.
Traced: The supplying of auxiliary heat to a pipe or piece of equipment by means of a companion line: containing a hot fluid or electric resistance. It can be thermally or mechanically bonded to the: pipe or equipment.
Transference, Thermal: The steady-state heat flow from (or to) a body through applied thermal insulation and to (or: from) the external surroundings by conduction, convection, and radiation. It is expressed as the: time rate of heat flow per unit area of the body surface per unit temperature difference between: the body surface and the external surroundings.
Transmission, Heat: The quantity of heat flowing through unit area due to all modes of heat transfer induced by the: prevailing conditions.
Transmittance, Thermal (U-value): The combined thermal value of all the materials in a insulation system, air spaces, and surface air: films. The heat transmission in unit time through unit area of a material or construction and: boundary air films, induced by unit temperature difference between the environments on each: side. The I-P units are Btu / (hr – sq ft – deg F temperature difference) and the SI units are W /: (sq m – deg C temperature difference). Note: This heat transmission rate has been called the: overall coefficient of heat transfer.
T-Rating: A rating usually expressed in hours indicating the length of time that the temperature on the nonfire: side of a fire-rated assembly exceeds 325°F above its ambient temperature as determined by: ASTM E-814 (UL-1479).
Tube Turn (Bend): Pipe, factory or field formed, to pre-determined radii.
UL: Underwriters Laboratories. An independent materials testing company. UL provides testing,: evaluation, and listing services for products having specific safety-related features. UL test: standards generally are similar to ASTM International standards when both exist.
ULTRAVIOLET LIGHT: Resistance to ultraviolet light is significant if application is outdoors.
Underground: Insulation applied on piping and equipment located below grade and in direct contact with the: surrounding soil.
Union: A coupling device for connecting pipes.
Urethane: Plastic foam of rigid polyurethane closed-cell insulation in board, pipe insulation or foamed-inplace: form.
U-Value (Transmittance): See Transmittance, Thermal (U-value): Valve: Any of various devices that regulate liquid or gas flow by opening, closing or obstructing its: passage.
VALVE: Any of various devices that regulate liquid or gas flow by opening, closing or obstructing its passage.
VAPOR DRIVE: Moisture vapor drive occurs as warmer, more humid air is drawn to colder surfaces and seeks to penetrate (or "drive") into the insulation. Vapor drive is greatly influenced by temperatures; hotter water vapor is more effective at penetrating barriers than cooler water vapor.
VAPOR-RETARDER JACKET: Any material or composite meeting the requirements of a vapor retarder and used for the finish of insulation material. It may be factory furnished or field applied.
VAPOR-RETARDER: Vapor retarders inhibit moisture from traveling to lower temperature surfaces where it may condense. A vapor retarder material is usually a jacket or coating.
Ventilating Air: Air supplied to or removed from any space by natural or mechanical means.
Ventilating Duct: Duct supplying or removing air by natural or mechanical means.
Vermiculite: Insulation composed of natural vermiculite ore expanded to form an exfoliated structure.
Vertical Piping: Any piping that is less than 45° from the vertical plane.
Vibration Resistance: The property of a material that indicates its ability to resist mechanical vibration without wearing: away, setting or dusting.
Vinyl: The name of a class of resins or sheeting.
Warpage: The change in the flatness of a material caused by differences in the temperature and/or humidities applied to opposite surfaces of the material.
Washer (Insulation Clip): Self-locking flat metal device applied to anchor pins to secure the insulation in place.
Water Absorption: The increase in weight of a material expressed as a percentage of its dry weight or volume after: immersion in water for a specified time.
Water Resistant: Capable of withstanding limited exposure to water.
Water Vapor Diffusion: The process by which water vapor spreads or moves through permeable materials caused by a: difference in water vapor pressure.
Water Vapor Permeability: The time rate of water vapor transmission through unit area of flat material of unit thickness: induced by unit vapor pressure difference between two specific surfaces, under specified: temperature and humidity. Water vapor permeability is measured in the IP system in perm: inches.
Water Vapor Permeance: The time rate of water vapor transmission through unit area of flat material or construction: induced by unit vapor pressure difference between two specific surfaces, under specified: temperature and humidity conditions. Water vapor permeance is measured in IP system in units: of perm.
Water Vapor Pressure: The pressure of water vapor at a given temperature; also the component of atmospheric pressure: contributed by the presence of water vapor.
Water Vapor Resistance: The steady state vapor pressure difference that induces unit time rate of vapor flow through unit: area of a flat material (or construction that acts like a homogeneous body) for specific conditions: of temperature and relative humidity at each surface.
 Water Vapor Resistivity: The steady state vapor pressure difference that induces unit time rate of vapor flow through unit: area and unit thickness of a flat material (or construction that acts like a homogeneous body), for: specific conditions of temperature and relative humidity at each surface.
Water Vapor Retarder (Barrier): A material or system that significantly impedes the transmission of water vapor under specified: conditions.
Water Vapor Retarder Jacket: Any material or composite meeting the requirements of a water vapor retarder and used for the: jacketing of insulation material. It may be factory furnished or field applied and may or may not: be adhered to the insulation material.
Water Vapor Transmission Rate (WVTR): The steady state water vapor flow in unit time through unit area of a body, normal to specific: parallel surfaces, under specific conditions of temperature and humidity at each surface. The I-P: units are lbs / hr – ft2; the SI units are grams / hr – m2.
Waterproof: Impervious to prolonged exposure to water or water entry.
Weather Barrier: A breather jacket or coating which allows passage of water vapor yet protects from atmospheric: conditions.
Weather/Vapor-Retarder (barrier): A vapor retarder that also protects from atmospheric conditions.
Weld Pin: Made of carbon steel, stainless steel or aluminum in various lengths for attaching insulation to: metal surfaces. Applied by welding, usually with a weld gun.
Wetting and Adhesion, Surface: The mutual affinity of and bonding between finish and the surface to which it is applied.
Wicking: Action of absorbing by capillary action.
Wood Fiber: Insulation composed of wood/cellulosic fibers, with or without binders.