Forced-Entry Resistant Laminates

Forced-entry resistant laminates are security glazing systems engineered to resist sustained physical attack and delay the creation of an opening through which an attacker can gain access.

Unlike conventional glazing, the objective is not simply to resist the first impact or prevent the glass from cracking.

In many forced-entry constructions, glass fracture is expected.

The engineering challenge is to keep the damaged glazing functioning as a barrier as the attack continues.

Glass, polycarbonate, acrylic, and transparent interlayers can be combined in different ways to retain fractured material, distribute impact loads, resist penetration, and make it progressively more difficult for an attacker to create or enlarge an opening.

Depending on the construction and testing, forced-entry resistant laminates may also provide ballistic resistance.

There is no single material combination that defines forced-entry glazing.

Engineering Principle

Forced-entry resistance is a performance objective, not a material recipe.

What Is a Forced-Entry Resistant Laminate?

A forced-entry resistant laminate is transparent security glazing designed to resist repeated physical attack for a defined test condition.

The construction may incorporate different combinations of:

• Glass
• Polycarbonate
• Acrylic
• Structural interlayers
• Surface treatments
• Specialty transparent materials

The exact architecture depends on the threat being addressed.

Some constructions rely heavily on glass and structural interlayers.

Others incorporate polycarbonate because of its toughness, deformation capability, and penetration resistance.

Still others use laminated polycarbonate or combinations of polycarbonate and acrylic.

These technologies can look similar when installed, but they may behave very differently under attack.

The materials alone therefore do not establish forced-entry performance.

Testing of the complete construction establishes demonstrated performance against a defined threat.

Forced Entry Is About Delay, Not Preventing All Damage

A common misconception is that security glazing has failed once it cracks.

That is not necessarily true.

In a forced-entry resistant laminate, cracking can occur relatively early in an attack while the laminate continues functioning as a security barrier.

As impacts continue:

• Glass may fracture
• Acrylic may crack
• Polycarbonate may deform
• Interlayers may stretch
• The impact area may become opaque
• Pieces of material may become heavily damaged
• The panel may experience substantial permanent distortion

The critical question is whether the attacker can convert that damage into a breach or usable opening.

This distinction is fundamental to forced-entry engineering.

Engineering Principle

The purpose of forced-entry resistant glazing is not to prevent the first crack. It is to maintain the barrier as damage accumulates.

How Laminated Security Glazing Continues Working After Breakage

Conventional glass can lose much of its ability to function as a barrier after fracture.

Laminated security glazing behaves differently.

Transparent interlayers bond the individual materials together and help retain fractured components after impact.

As damage accumulates, the laminate may continue resisting penetration because the remaining materials still form an interconnected barrier.

Depending on the construction:

• Fractured glass can remain bonded to the interlayer.
• Interlayers can stretch rather than immediately tear.
• Polycarbonate can deform while remaining intact.
• Acrylic can fracture internally while surrounding layers maintain containment.
• Loads can be transferred into a larger area of the panel.
• Multiple layers can continue resisting the attack after individual components have been damaged.

This ability to remain functional after visible damage is one of the defining characteristics of an effective forced-entry laminate.

Engineering Insight

Security glazing should not be judged solely by how much damage it sustains. It should be judged by how effectively it continues functioning after that damage occurs.

Materials Commonly Used in Forced-Entry Laminates

Different materials contribute different characteristics to a forced-entry construction.

Glass

Glass can provide:

• Hardness
• Rigidity
• Surface durability
• Scratch resistance
• Architectural appearance
• Initial impact resistance
• Resistance to certain cutting and penetration methods

Glass can fracture under sustained attack, but when properly laminated, the fractured glass can remain part of the security barrier.

Polycarbonate

Polycarbonate contributes:

• Toughness
• Flexibility
• Impact-energy absorption
• Penetration resistance
• Deformation capability
• Material retention

Its ability to undergo substantial deformation without immediately losing integrity makes polycarbonate particularly useful in repeated-impact applications.

Acrylic

Acrylic can contribute:

• Rigidity
• Optical clarity
• Dimensional stability
• Lower density than glass
• A different mechanical response to impact

Acrylic may fracture under severe attack while surrounding materials continue maintaining the barrier.

Interlayers

Interlayers can:

• Bond materials together
• Retain fractured material
• Transfer loads
• Stretch during impact
• Help prevent damaged areas from becoming openings
• Allow multiple layers to continue working as a system

Engineering Principle

Every material has a purpose. Every layer has a job.

Glass-Based Forced-Entry Laminates

Glass-based forced-entry laminates can use multiple glass plies bonded with structural interlayers.

When struck repeatedly, the glass may fracture, but the interlayers retain the broken material and help prevent the attacker from rapidly clearing the opening.

The resulting fractured mass can continue presenting resistance.

Depending on the construction, additional impacts may be required to:

• Break additional glass
• Stretch or tear the interlayer
• Dislodge retained fragments
• Penetrate the laminate
• Enlarge the damaged area
• Create a usable opening

Glass-based constructions can provide important architectural advantages, including a hard exposed surface, familiar cleaning characteristics, and conventional architectural appearance.

Their forced-entry performance, however, should be established through testing rather than inferred from glass thickness or ply count.

Glass + Polycarbonate Constructions

Polycarbonate can also be incorporated into glass-based forced-entry laminates.

This combines the hardness and rigidity of glass with the toughness and deformation characteristics of polycarbonate.

During repeated attack:

• Glass can resist initial impacts and cutting action.
• Glass fracture can distribute impact energy.
• Interlayers retain fractured glass.
• Polycarbonate can flex and absorb additional energy.
• Polycarbonate can make complete penetration more difficult.
• The composite construction can continue resisting after significant glass damage has occurred.

This is another example of why security glazing should be understood as a system.

Glass and polycarbonate do not need to behave similarly.

Their different characteristics can be complementary.

Laminated Polycarbonate and Polycarbonate/Acrylic Constructions

Forced-entry resistance can also be achieved using polymer-based laminate architectures.

Laminated polycarbonate uses multiple polycarbonate plies and urethane interlayers to create a tough, highly impact-resistant barrier.

Polycarbonate and acrylic laminates combine the deformation and toughness of polycarbonate with the rigidity and optical characteristics of acrylic.

These constructions can offer advantages including:

• High impact resistance
• Strong penetration resistance
• Resistance to repeated attack
• Relatively low weight
• No glass spall
• Significant deformation without immediate barrier loss

Their exposed surfaces and maintenance requirements differ from conventional glass, however, and should be considered as part of the complete application.

Engineering Insight

Different laminate architectures can achieve forced-entry resistance through different mechanical mechanisms.

The Role of Interlayers

Interlayers are central to the performance of many forced-entry laminates.

Without an effective interlayer, fractured transparent materials may lose cohesion and be more easily removed from the opening.

A properly engineered interlayer can help:

• Retain broken glass
• Transfer impact loads
• Maintain continuity after fracture
• Resist tearing
• Accommodate deformation
• Bond dissimilar materials
• Slow removal of damaged material

Different interlayer technologies have different mechanical characteristics.

Stiffness, elongation, adhesion, thickness, temperature response, and material compatibility can all influence laminate behavior.

The appropriate interlayer therefore depends on the complete construction and performance objective.

Engineering Principle

In forced-entry glazing, the interlayer can become increasingly important after the glass has already broken.

How Repeated Attack Differs from Ballistic Impact

Ballistic and forced-entry threats place very different demands on glazing.

A ballistic event typically involves extremely high energy delivered over a very short period.

A forced-entry attack can occur over a much longer period and may involve repeated impacts directed at an increasingly damaged area.

An attacker may:

• Strike the same location repeatedly
• Move impacts around the damaged area
• Attempt to dislodge fractured material
• Use sharp tools
• Use blunt tools
• Attempt to cut or tear exposed interlayers
• Exploit an existing hole
• Try to enlarge the opening

The glazing therefore needs more than initial impact strength.

It needs damage tolerance.

Why Damage Tolerance Matters

Damage tolerance describes the ability of a system to continue performing after damage has occurred.

This concept is especially important in forced-entry glazing.

A material that is extremely hard but loses integrity rapidly after fracture may behave differently from a laminate that sustains greater visible damage but continues resisting penetration.

Forced-entry performance therefore involves questions such as:

• Does fractured material remain retained?
• Can the attacker remove damaged material?
• Does an initial opening propagate rapidly?
• Can the interlayer continue carrying load?
• Can the attacker enlarge the opening?
• Does the remaining laminate continue resisting impact?
• How does the surrounding framing retain the damaged glazing?

Engineering Principle

In forced-entry glazing, damage tolerance can be more important than damage prevention.

Creating and Preventing a Usable Opening

A forced-entry attack generally has a practical objective: create enough of an opening to gain access through the barrier.

That makes the concept of a usable opening more meaningful than cosmetic damage alone.

A laminate may be:

• Completely cracked
• Heavily fractured
• Locally penetrated
• Permanently deformed
• Optically destroyed in the impact area

and still continue preventing passage.

Different test standards define failure and passage conditions differently, so the applicable test method must always be consulted.

But the broader engineering principle remains consistent:

Engineering Insight

A hole is not necessarily a breach, and visible destruction is not necessarily failure. The important question is whether the defined passage or penetration condition has been achieved.

Forced-Entry vs. Bullet-Resistant Glazing

Forced-entry resistance and bullet resistance address different threats.

Bullet-resistant glazing is engineered primarily to stop specified ballistic projectiles under defined impact conditions.

Forced-entry resistant glazing is engineered to resist sustained physical attack and delay intrusion.

A construction can provide:

• Ballistic resistance without a particular forced-entry classification
• Forced-entry resistance without ballistic resistance
• Both ballistic and forced-entry resistance

One performance should not be inferred from the other.

A thick laminate is not automatically bullet resistant.

A bullet-resistant laminate is not automatically forced-entry resistant.

A forced-entry laminate is not automatically bullet resistant.

Specification Insight

“Security glazing” is not a performance rating. The required threat must be defined.

Combining Forced-Entry and Ballistic Performance

Some applications require both projectile resistance and continued resistance to physical attack.

This can be especially important when an attacker may use a firearm to damage the glazing and then attempt to physically penetrate the weakened area.

Multi-threat laminate design may therefore consider:

• Projectile penetration
• Protected-side fragmentation
• Residual barrier integrity
• Repeated impact
• Interlayer retention
• Penetration resistance after damage
• Ability to prevent enlargement of an opening

A construction should be tested against the threats that matter for the project.

Engineering Principle

Passing a ballistic test does not establish forced-entry performance, and passing a forced-entry test does not establish ballistic performance.

ASTM F1233 — Progressive Forced-Entry Resistance

ASTM F1233 provides a recognized framework for evaluating security glazing and systems against defined security threats.

For forced-entry engineering, one of its important contributions is the concept of subjecting a specimen to prescribed attack conditions and evaluating whether the attacker can achieve the defined passage condition.

The standard can address different threat mechanisms and attack sequences.

This makes it useful for understanding how glazing behaves as damage accumulates rather than judging performance from the first visible crack.

The achieved test sequence and classification matter.

Simply stating that a product is “tested to ASTM F1233” does not provide enough information to understand its demonstrated performance.

Detailed treatment of the standard belongs in PA-TS-002 — Understanding ASTM F1233.

ASTM F3561 — Ballistic Weakening Followed by Forced Entry

ASTM F3561 addresses a different security problem.

In an active-shooter scenario, an attacker may first fire at the glazing and then physically attack the damaged area in an attempt to gain entry.

This means the laminate must continue resisting after ballistic impacts have already altered or weakened the construction.

That creates a different engineering challenge from conventional forced-entry testing.

The sequence is important:

Ballistic damage occurs first. Physical attack follows.

The resulting performance therefore depends on the laminate’s residual integrity after the ballistic portion of the test.

Engineering Insight

For active-shooter glazing, the important question is not simply whether the glazing survives the bullet impacts. It is whether the damaged barrier can continue delaying entry afterward.

Detailed treatment of this standard belongs in PA-TS-003 — Understanding ASTM F3561.

ASTM F1915 — Detention and Correctional Security Glazing

ASTM F1915 addresses security glazing for detention and correctional environments.

The threat environment is distinctly different from a school, storefront, bank, or conventional commercial building.

Detention glazing may be subjected to:

• Repeated abuse
• Sustained blunt impacts
• Sharp impacts
• Attempts to create an escape opening
• Temperature extremes
• Thermal attack
• Continued attack after significant damage has already occurred

ASTM F1915 evaluates glazing through prescribed impact and environmental conditions intended to assess its ability to resist this type of institutional security threat.

The standard includes multiple security grades, with Grade 1 representing the most demanding level and Grade 4 the least demanding.

Its testing can include repeated large blunt and sharp impacts, cold and warm conditioning, and a torch combined with small blunt impacts.

As with other forced-entry testing, the appearance of the specimen after attack does not by itself determine whether the glazing has failed.

A central question is whether the attack creates the defined forcible-egress opening.

This reinforces a broader principle that applies throughout forced-entry engineering:

Engineering Principle

The condition of the damaged glazing matters less than whether the attacker has achieved the defined breach or passage criterion.

ASTM F1915 should not be treated as a universal forced-entry standard for all buildings. It addresses the particular security requirements of detention and correctional facilities.

Detailed treatment belongs in PA-TS-004 — Understanding ASTM F1915.

Different Threats Require Different Tests

ASTM F1233, ASTM F3561, and ASTM F1915 all involve forms of physical attack, but they do not evaluate the same security problem.

At a high level:

ASTM F1233 evaluates defined security threats and progressive attack conditions.

ASTM F3561 addresses forced-entry resistance following ballistic weakening associated with an active-shooter threat.

ASTM F1915 addresses sustained abuse and escape-related threats in detention and correctional environments.

They should not be treated as interchangeable certifications or different “levels” of the same test.

Engineering Principle

“Forced-entry resistant” is not a complete performance description. The relevant question is: resistant to what type of attack, tested by what method, and to what performance level?

The Importance of the Complete Glazing System

A security laminate does not function independently of the system holding it in place.

The surrounding assembly can include:

• Framing
• Glazing stops
• Bite or engagement
• Gaskets
• Structural sealants
• Anchors
• Fasteners
• Mullions
• Door hardware
• Adjacent wall construction

A strong laminate installed in an inadequate retention system may not provide the intended overall security performance.

An attacker does not have to defeat the center of the glazing if the edge, frame, stop, or surrounding assembly provides an easier path.

The relationship between glazing and framing therefore matters.

Patriot Armor manufactures security glazing, while framing and complete system integration may be provided by other manufacturers, fabricators, or installation partners.

The performance claim should accurately reflect what was actually tested.

Engineering Insight

A security opening is a system. The attacker only needs to defeat its weakest effective path.

Thickness Alone Does Not Define Forced-Entry Performance

It is tempting to compare security glazing by thickness.

That can be misleading.

Two laminates of similar thickness may use:

• Different materials
• Different numbers of plies
• Different interlayers
• Different layer sequences
• Different polycarbonate grades
• Different acrylic components
• Different glass treatments

and may therefore behave very differently under attack.

Likewise, a thicker construction is not automatically more resistant to every forced-entry threat.

Engineering Principle

Thickness describes geometry. Testing describes demonstrated security performance.

Optics, Weight, Maintenance, and Architectural Tradeoffs

Forced-entry resistance is only one requirement of a finished glazing system.

The selected technology may also need to satisfy:

• Optical clarity
• Weight limitations
• Panel size
• Surface durability
• Scratch resistance
• Cleaning requirements
• Chemical compatibility
• Thermal performance
• Solar control
• Low-E requirements
• Architectural appearance
• Framing limitations
• Installation requirements
• Life-cycle expectations

Different laminate architectures create different tradeoffs.

Glass-based laminates may offer a familiar, hard service surface.

Polycarbonate-containing laminates may offer substantial toughness and weight advantages but require greater attention to cleaning and chemical compatibility.

Acrylic-containing systems may provide another balance of rigidity, optics, weight, and impact behavior.

The appropriate technology depends on the complete project.

Typical Applications

Forced-entry resistant laminates may be appropriate where delaying unauthorized entry is an important security objective.

Applications can include:

• Schools and educational facilities
• Government facilities
• Corporate offices
• Financial institutions
• Banks
• Retail environments
• Luxury storefronts
• Places of worship
• Public buildings
• Critical infrastructure
• Data centers
• Security checkpoints
• Guard booths
• Transportation facilities
• Detention and correctional facilities where the applicable detention requirements are addressed
• Other high-security openings

The appropriate test standard and laminate construction should follow the threat assessment for the specific application.

Testing and Performance Documentation

Forced-entry performance should be associated with the specific construction and test method evaluated.

Useful documentation may identify:

• Test standard
• Test sequence
• Security grade or classification
• Passage criterion
• Threat or attack method
• Number of impacts
• Impact energy
• Tools or impactors
• Ballistic conditioning where applicable
• Environmental conditioning where applicable
• Specimen dimensions
• Laminate construction
• Framing or retention system
• Test result
• Test laboratory
• Certification or listing status where applicable

The wording of a security claim matters.

“Forced-entry resistant” by itself provides limited information.

A more useful claim identifies the applicable standard and achieved performance classification.

Specification Insight

The more precisely the threat and test result are described, the more meaningful the security claim becomes.

Selecting the Appropriate Construction

The selection process should begin with the threat.

Questions may include:

• Is the primary concern opportunistic physical attack or a sustained deliberate attack?
• Are blunt tools expected?
• Are sharp tools relevant?
• Is ballistic attack part of the threat?
• Must the glazing continue resisting physical attack after ballistic damage?
• Is the application detention or correctional?
• What constitutes failure for the project?
• How much intrusion delay is required?
• Is protected-side spall acceptable?
• What are the panel dimensions?
• What framing system will retain the glazing?
• What optical requirements apply?
• Are there weight limitations?
• What environmental conditions will the glazing experience?
• What maintenance practices are expected?

Once these requirements are understood, an appropriate laminate architecture and validated test performance can be selected.

The Wrong Question

What is the strongest forced-entry glass?

A Better Question

What glazing construction and system have demonstrated the appropriate resistance to the specific attack scenario the project is designed to address?

Key Takeaways

• Forced-entry resistant glazing is engineered to delay intrusion and resist the creation of a usable opening.
• Forced-entry resistance is a performance objective, not a single material recipe.
• Glass fracture does not automatically represent failure.
• Effective forced-entry laminates are designed to continue functioning as damage accumulates.
• Glass, polycarbonate, acrylic, and interlayers can contribute different mechanical functions.
• Interlayers become particularly important after brittle materials have fractured.
• Damage tolerance is a central characteristic of forced-entry glazing.
• A heavily damaged laminate can continue functioning as a security barrier.
• Ballistic resistance and forced-entry resistance are different performance characteristics.
• Some constructions can provide both, but each required performance should be validated.
• ASTM F1233, ASTM F3561, and ASTM F1915 address different physical-attack environments and should not be treated as interchangeable.
• ASTM F1233 provides a framework for defined progressive security threats and passage criteria.
• ASTM F3561 addresses physical attack after ballistic weakening associated with active-shooter scenarios.
• ASTM F1915 addresses detention and correctional security glazing subjected to sustained abuse and escape-related threats.
• Visible damage is not necessarily the same as achieving the defined breach or passage condition.
• The glazing and retention system should be considered together.
• Thickness alone does not establish forced-entry performance.
• Optical quality, weight, surface durability, maintenance, building performance, and life-cycle requirements remain part of the engineering decision.
• Security performance belongs to the tested construction and system, not simply to the material name.

Continue Learning

PA-TS-002 — Understanding ASTM F1233

Explore the test sequences, threat classifications, and passage criteria used to evaluate security glazing against defined forced-entry threats.

PA-TS-003 — Understanding ASTM F3561

Learn how active-shooter glazing is evaluated through ballistic weakening followed by forced-entry impacts.

PA-TS-004 — Understanding ASTM F1915

Explore how glazing for detention and correctional facilities is evaluated against repeated impacts, environmental conditioning, thermal attack, and forcible-egress criteria.

PA-EF-002 — What Is Forced-Entry Resistant Glass?

Learn the fundamental principles behind glazing designed to delay physical intrusion.

PA-EF-005 — Bullet-Resistant vs. Forced-Entry Resistant Glazing

Understand why ballistic resistance and forced-entry resistance address different threats.

PA-PT-004 — Laminated Polycarbonate

Explore how multiple polycarbonate plies and urethane interlayers can provide high resistance to repeated physical attack.

PA-PT-005 — Polycarbonate & Acrylic Laminates

Learn how polycarbonate and acrylic can be combined to balance toughness, rigidity, optics, weight, and security performance.

PA-MC-005 — Understanding Glass-to-Glass Interlayer Technologies

Explore how interlayer selection affects retention, stiffness, impact behavior, and laminate performance.