Everything you wanted to know about auto glass, but were afraid to ask.

At Speedy Glass, we want you to make an informed choice. Below you’ll find an alphabetical list which we hope will help answer some of your questions about the terms and technology of auto glass repair and replacement.


Acute Area

The area of the windshield directly in front of the driver’s eyes, beginning just above the steering wheel. It measures approximately 8 1/2 inches high by 11 inches wide. This area is used as the standard for the driver’s critical vision area by most auto glass shops and insurance companies in North America.


The clinging or sticking together of two surfaces. The ability of an adhesive to stick to a surface.

Adhesive Failure

Adhesive failure indicated by the material’s failing (pulling loose) at the surface of the substrate. Similar to “scotch” tape peeling off a plastic substrate.


Any substance that is capable of bonding other substances together by surface attachment. In an auto glass replacement context, it is a high-strength polyurethane material unless otherwise specified.


The branch of physics that deals with the motion of a solid body through air and other gases.


The progressive change in the chemical and physical properties of a sealant or adhesive over time.


A passive restraint system that uses an explosive device to inflate a bag at a high rate of speed. The bag inflates with a gas and then quickly deflates when a vehicle occupant is thrown into it. It is mounted in the steering wheel on the driver’s side of the vehicle and in the dashboard on the passenger’s side. There are also airbags installed for side impact collisions. Some passenger-side airbags use the windshield to position the deploying bag.

Air Side

The upper surface of the glass, also referred to as the score side.


The controlled process of cooling glass after manufacturing to strengthen glass and make it less brittle.


The controlled process for making glass stronger and less brittle in which the glass is heated and then cooled.


The forward or windshield pillars on a car that support the windshield and the front portion of the roof.

Antenna Glass

In some late-model vehicles the radio antenna is incorporated into the windshield or the back-lite (rear window).

Anti-Lacerative Glass

Glass that has a resilient layer (PVB) added to the inner surface. It prevents passengers from coming into contact with broken glass edges on the inner surface in the event of a collision.


An abbreviation of the after market auto glass industry. Automotive Replacement Glass/After market Glass Replacement.

Auto Glass Repair

The act of repairing a break in a windshield or other laminated auto glass part, rather than replacing it. Auto glass repair is a permanent process that removes the air from the break and fills it with a curable, optically matched resin. Same as windshield repair.


Passenger car rear window made of tempered or laminated glass. Vehicles with convertible tops have windows made of plastic or tempered.


A sealant or adhesive compound after application in a joint, irrespective of the method of application, such as a urethane bead applied to a pinchweld. A bead looks like a ribbon of adhesive rather than a round drop of adhesive.

Belt Molding

A rubber molding between the inner and outer panels of a vehicle door through which the door glass is raised and lowered.


Amount of adhesive overlap between the pinchweld and windshield.

Block (setting)

A small piece of neoprene or other suitable material used to position glass in the frame.


The side or door posts connect the sills and the roof, providing the car’s roof support. On a true hardtop designed car-a term derived from hardtop convertible-these pillars are missing, leaving uninterrupted glass along the sides of the car.

Bullet-Resistant Glass

Glass that consists of multiple layers of laminated glass. It is designed to resist penetration from medium to super-power small arms and high-power rifles.

Bull’s Eye

Impact damage to laminated glass that is marked by a clean, separated cone in the outer layer of the glass.


An adhesive used in earlier model vehicles for glass retention. It is a petroleum product that requires no curing or hardening. Butyl is available in rolls of approximately 15 feet.

Butyl Rubber

A copolymer of isobutene and isoprene. As a sealant, it has low recovery and slow cure, but good tensile strength and elongation.

Caulk (noun)

A sealant with a relatively low movement capability.

Caulk (verb)

To fill the joints with a sealant.


A resilient mastic compound often having a silicone, bituminous, or rubber base; used to seal cracks, fill joints, prevent leakage, and/or provide waterproofing used in the replacement of commercial or residential glass.

Chemical Cure

Curing by chemical reaction. This usually involves the cross-linking of a polymer.

China Markers

A wax marker used to mark glass.


Impact damage to laminated glass that does not penetrate the outer lite. Although glass is missing from the impact point, there is no trapped air in the damage.

Close-Cut Or Partial-Cut Installation

An installation method that leaves most of the existing adhesive bead/bed adhered to the metal frame and adds a small fresh bead of adhesive into which to set the glass. Some vehicle manufacturers do not recommend this procedure.

Coated Glass

Glass with a chemical film applied to one surface. The film can provide such enhanced performance characteristics as privacy, solar or mirror effects.


The ability of a sealant or adhesive to hold itself together. The internal strength of an adhesive or sealant.

Cohesive Failure

Adhesive failure indicated by cured material on both substrate surfaces. The material itself failed (the body of the adhesive or sealant pulled apart).

Combination Break

A break in a windshield involving more than two types of breaks.


Refers to the reaction a sealant has on another sealant or on another material.


Pressure exerted on a sealant in a joint.


The act of pressing together or to force into a smaller space.


A substance, liquid or solid, which is present in a break. Contaminants must be removed from a break before a repair can begin.


A liquid used to cool and lubricate glass while it is being cut or ground with a tool to prevent hot spots or fracturing of the glass.


The chemical reaction of air, moisture, or corrosive materials on a surface; also called oxidation. The process of wearing away the surface of a solid.


An extended crack in a windshield from both sides of an impact point. There are several different kinds of cracks: Short crack: A crack on the windshield of 6 inches (15.24 cm) or less. Long crack: A crack on the windshield of more than 6 inches (15.24 cm). Edge crack: Any crack on the windshield that extends to an edge. Floating crack: Any crack on the windshield that does not extend to an edge. Stress crack: Any crack extending from an edge without an impact point.

Cure Time

The time required for a chemical or material to dry or set at a given temperature and humidity. Cure time varies with the type of material used and the thickness of the application.

Curing Agent

A chemical which is added to effect a cure in a polymer.


A process of drying and hardening over a given period.


A product having several purposes: 1. A dam positions the glass in the opening while the adhesive cures. 2. A dam holds the liquid adhesive and prevents it from flowing into the interior of the vehicle. 3. A dam provides an esthetically pleasing site-line. 4. A dam acts as a sound barrier.


Same as break and crack.


A disposable cotton applicator for applying primers and preps to the metal and glass bonding surfaces.


The failure of the bond between layers, as when windshield glass separates from the laminate, or when paint peels from the substrate beneath it.


A term often used by the public to refer to stone damage to a windshield.

Double Seal Units

Insulating glass with two separate seals used to form the seal of the glass.

Drop-Jaw Glass Pliers

Pliers used for breaking glass. They have a flat upper jaw and humped lower jaw.

Dry Glazing

A method of securing glass in a frame by use of a dry, preformed, resilient gasket.


A blunt probe used to penetrate sealants that measures the shore hardness from 0 to 100.

Edge Crack

Any crack on the windshield that extends to an edge. See also: Crack.


The ability of a material to return to its original shape after it has been stretched.


Is the stretchability or flexibility of cured urethane. Urethane must have the right flexibility to absorb body flex and the stiffness to support glass.


A granular mineral substance used for grinding and polishing glass.

Encapsulated glass

A type of auto glass fabrication. Pre-assembled parts that contain hardware: moldings, fasteners, clips, or gaskets. Glass with a decorative molding around all or part of the perimeter. The encapsulation can also act as a channel guide. The molding (encapsulation) is actually part of the glass and can be removed only by cutting it off the glass.

Extrusion Failure

The failure which occurs when a sealant is forced too far out of the joint.

Fast Cure Urethane

A faster hardening adhesive. The term “fast” is relative to the surrounding temperature and humidity. Curing time is faster than for normal adhesives.

Fatigue Failure

The failure of a material due to rapid cyclic deformation.

Federal Motor Vehicle Safety Standards (FMVSS)

A series of standards required of the automobile manufacturers by the U.S. Government. All new vehicle models must meet these standards before they are allowed to be sold in the United States.

Filler Strip

A strip inserted into a rubber gasket after the glass is installed, forcing the gasket against the glass to form a seal and improve the grip. It is sometimes called locking a bead or spline.


Finely ground material added to a sealant or adhesive to change or improve certain properties.


A method of gaining access to a tight break by flexing the glass back and forth, either with a tool or by hand.

Floating Crack

Any crack on the windshield that does not extend to an edge. See also: Crack.


A flower petal effect around the outer edge of a repair. This is caused by the laminate detaching from the outer layer of glass.


The painted band around the perimeter of auto glass parts. Protects the urethane bead from UV degeneration.

Full Strip Installation

An installation method whereby the technician removes the existing bed/bead of adhesive from the vehicle frame. Approximately 1-2 mm of old adhesive remains. The technician applies new/fresh adhesive on top, then sets the glass into the fresh adhesive.


A seal, usually of rubber, that holds a piece of auto glass to the vehicle body. There are various sizes and shapes of glass part gaskets, depending on vehicle design.

Green Strength

A term used by some adhesive manufacturers to describe initial strength of an adhesive.

Gun-Grade (gunnable sealant)

Sealant that can be applied with a manual caulking gun.

Half Moon

Damage to a windshield that has a half-circle separation around the impact point. It is similar to a bull’s eye.

Hand Seamer

A hand tool used to seam the edge of glass and plastic.


The fabric which lines the roof of a vehicle’s passenger compartment.

Heat Strengthened Glass

Similar to tempered glass, it is made by heating annealed glass, then cooing it more slowly than tempered glass.

Heated Urethane

A type of adhesive that is heated to a prescribed temperature before application. The heat pre-cures the adhesive faster, so the car can be released sooner.

High Modulus

High modulus is a rigidity requirement of cured adhesive. It provides extra strength to resist torsional twisting.

Hot Melt Butyl

An insulating glass edge sealant used during manufacturing.


This is the most common break. It occurs when an object hits the windshield.

Impact Resistance

The measurement by which it is determined how much impact is required for breakage.

Impact Site

The actual location on the outside layer of glass, where it was struck by an object (usually a stone). Typically a small piece of glass is missing.


Another name for laminated glass (see laminated glass).


Vinyl inner layer of laminated glass.

Laminated Glass

A type of safety glass that has a layer of plastic bonded between layers of glass. Laminated glass is used mainly for windshields.

Lap Joint

A joint in which the component parts overlap so that the sealant or adhesive is placed into shear action.

Lap Shear Strength

The strength demonstrated by the diagonal pull of two substrates until adhesive failure. The name comes from the lap joint created by the test samples and the shear action used to pull the samples apart.


Short cracks that emanate from a break.

Light Transmittance

The percentage of visible light able to pass through the glass.


A term for a pane or a finished piece of glass.

Load Distribution

The specific placement of a supported weight or mass in a given area.

Long Crack

A crack on the windshield of more than 6 inches (15.24 cm). See also: Crack.

Mobile Unit

A vehicle, usually a van or light truck, properly equipped with repair, replacement and safety equipment and tools, driven to an auto glass repair customer’s home or place of business. Repairs are made from the vehicle.


The ratio of strength to stress.


A synthetic rubber having physical properties closely resembling those of natural rubber but not requiring sulphur for vulcanization. Extremely good weather resistance (both heat and cold) with ultraviolet stability.


Abbreviation for “original equipment manufacturer.”

One-Part Urethane

An adhesive used in auto glass replacement that has only one component.


A material, either film or liquid, that is applied to the back of a piece of glass to act as a light shield.


As in “Open-celled foam.” Foam extrusions can have the body contain connecting open cells. This allows air to pass through the foam to promote adhesive cure.

Open Time

The time interval between the application of an adhesive and when it becomes no longer workable.

Passive Restraint System

A system of protection that requires no effort on the part of the occupants of a vehicle, i.e., self-retracting seat belts, airbags.

Personal Protective Equipment (PPE)

The safety gear worn by an auto glass repair technician. It includes nitrile gloves, safety/U-V glasses, dust and mist mask (dual strap), first aid kit, and any additional equipment required by company policy.

PIB tape

Poly-Isobutylene Tape; used to form the primary seal of a dual seal insulating glass unit.


A type of metal weld joint. In the auto glass industry, the pinchweld is the part of the vehicle frame where the glass adheres.


The impact point from which, typically, a small piece of glass is missing.


A material which softens a sealant or adhesive by solvent action.

Plate Glass

Flat glass whose surface has been ground and polished until it is free of distortion. Most plate glass manufacturing ceased when the float glass process was developed (see float glass).

Poly Vinyl Butyral

Vinyl inner layer of laminated glass.


A compound consisting of long chain-like molecules. The building units in the chain are monomers.

Polyvinyl Butyral (PVB)

A plastic film used in laminated glass.


A cleaner or a product that enhances an adhesive. A prep is usually applied to the glass prior to the primer.

Pressure Sensitive Adhesive

Adhesive which retains tack after release of the solvent, so that it can be bonded by simple hand pressure.


An undercoat or chemical applied to a surface to improve the adhesion, durability, and appearance of a topcoat or the bond of an adhesive. A product (chemical) used to prepare metal bonding areas and ensure a strong bond between the glass part and the adhesive.

Primerless Urethane

A type of urethane adhesive that requires no primer on the glass surface. Metal primers may be necessary.

Pump Gun

A device used for pumping sealants and adhesives.


See “polyvinyl butyral”.

Quarter Glass

Rear side windows in a vehicle.


A manually or power-operated device which rolls a vehicle’s window up and down.


A solid organic material, generally not soluble in water, which has little or no tendency to crystallize. Resin is optically matched to auto glass, and is used to fill chips and cracks.

Reveal Molding

Chrome or plastic molding which fits over and covers the edges of the windshield and back glass.

Roll Bar

A hoop of tubular steel installed behind the driver, extending above the head and across the car. It helps protect the driver from injury if the car rolls over.

Roll Cage

A tubular steel structure incorporating a roll bar plus additional bars along the doors, windshield header, roof rails, etc., built into some racing cars to help protect the driver if the car rolls over, is impacted by another car or crashes.

Safety Glass

A general term used for either laminated or tempered glass. Only glass which has been laminated, however, can specifically be called laminated safety glass.


The term used to describe a “cut” on the surface of a glass or mirror with a glass cutter.


Any material used to seal joints or openings against the intrusion or passage of any foreign substance, such as water, gases, air or dirt.


A surface coating generally applied to fill cracks, pores or voids in a surface.

Setting Block

A small piece of neoprene or other suitable material that positions the glass in the frame or opening. An automotive part on which the glass rests in place.

Shaded Glass

Laminated glass in which a dark color has been added to the top section of the inner vinyl layer to improve driver visibility in glare. The color typically becomes lighter as the tint travels down the glass.

Short Crack

A crack on the windshield of 6 inches (15.24 cm) or less.

Side and Back Glass

In the 1950s, tempered glass became mandatory on the side and rear windows of cars. (This glass is often referred to as lite.) Tempered glass is also considered safety glass. Upon impact it crumbles into rounded glass pebbles, instead of shattering into large dangerous pieces. Windshield glass is laminated. It can be repaired, but side and back glass must be replaced. Although tempered glass is harder to break than laminated glass, there is a good reason laminated glass windshields are mandatory in the United States. Tempered glass could explode in your face while you’re driving. However, in the event that your car rolls over after an accident and you are trapped, tempered glass is much easier to cut through. That is why side and back glass use tempered glass.


Passenger car side windows. As with all back and body glass, it is tempered glass, unlike the windshield, which is laminated.

Skinned Over

A very thin layer of semi-cured adhesive on the surface of curing adhesive.

Star Break

Damage to a windshield marked by various-sized cracks radiating from the central impact point.

Stone Chip

A chip on the outer layer of a laminated windshield. Typical stone chips are star breaks, bullseyes or combination chips.

Straight-Jaw Glass Pliers

Glass pliers that have identical upper and lower jaws.

Stress Cracks

Cracks resulting from unusual forces acting on the glass body.

Tempered Glass

A strong, break-resistant type of safety glass that, if broken, shatters into small granular pieces.

Tinted Glass

Glass to which a small amount of color has been added consistently throughout the glass. Batch tinting reduces glare and absorbs heat.


A crack which occurs when the windshield is twisted, either by flexing in the vehicle frame or because of improper mounting. It can be helped along if the windshield has a nick in the edge.

Unibody Construction

A type of automobile construction. The strength of unibody construction does not lie only in the structural frame but rather in the strength of the whole.

Ultra violet (UV) Light

Part of the light spectrum. Ultra violet rays can cause chemical changes in rubbery materials and polymers.


Any of several strong polymer adhesives that are used to install auto glass. Urethane adhesives are necessary to meet government standards for windshield retention in most late-model passenger vehicles.

Urethane Breakdown

Results when urethane is exposed to ultra-violet light. Urethane breakdown appears as a chalky black powder on the surface of the hardened adhesive.


Before 1919, early windshields were made from hand-cut glass. This was fine for protecting people from wind, but if any objects came flying their way…well, it wasn’t pretty. Then Henry Ford introduced laminated glass, two layers of glass held together by an inner layer of cellulose. This plastic layer absorbs much of the shock upon impact and keeps occupants from being ejected through the windshield. Laminated glass does not shatter. In many instances, damage to laminated glass can be repaired. All other car windows use tempered glass, which shatters into tiny pieces upon impact. These windows cannot be repaired, but must be replaced. Although tempered glass is harder to break than laminated glass, there is a good reason laminated glass windshields are mandatory in the United States. Tempered glass could explode in your face while you’re driving. However, in the event that your car rolls over in an accident and you are trapped, tempered glass is much easier to cut through. That is why body and back glass use tempered glass. Today, polyvinyl butyral (PVB), a high-strength vinyl, is used in windshields instead of inferior cellulose. The glass is held in place by urethane, the best adhesive for affixing windshields. Until the 1970s, installers used butyl, and some still do, but it has only a fraction of urethane’s strength and durability. By the 1980s, due to an energy crisis, manufacturers started to build cars out of lighter materials. Much of the car’s structural integrity, which was formerly supplied by the frame, was shifted to the shell, including the windshield. If you have a cracked or dinged windshield, the structural integrity of your vehicle is compromised.

Windshield Repair

The act of repairing a break in a windshield, or other laminated auto glass part, rather than replacing it. Windshield repair is a permanent process that removes the air from the break and fills it with a curable, optically matched resin.

Wired Glass

Made by feeding a welded wire net of a particular design into the molten glass just before it enters the roller.

Glossary Sources

Speedy Glass, The National Glass Association, The Glass Encyclopedia, The British Glass Manufacturers’ Confederation,,

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