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Overglaze Polycarbonate Retrofit: How It Works and What the Ratings Mean

An overglaze is a polycarbonate shield mounted in front of the glass you already have. It is often described with big words and bigger numbers. This post explains in plain language how it attaches, what the one independent forced-entry report we found actually shows, how to read UL 752 and ASTM F3561 ratings, and what to ask for before anything goes on your building. Where only the manufacturer says something, we say so.

Published October 4, 2026 · Armored Glass Solutions

The Basics

What an overglaze actually is: a second layer, not a film

Security window film is applied to the glass itself. An overglaze is a separate sheet of polycarbonate mounted on the building's existing frames, in front of the original glass. Impact Security, the manufacturer of DefenseLite, calls it "a clear security glazing system that installs over existing window and door glass." It says the system is additive: it "does not replace or remove existing glass, frames, gaskets, or hardware." That is why people consider it: the glass and frame stay, with no demolition of the opening.

The trade-off is that the original glass is still there, and the shield and its attachment become things you have to understand and maintain. According to the manufacturer, DefenseLite is custom made for every opening, and BulletShield is custom fabricated "based on perceived threat levels, budgets, and existing glazing conditions." Neither is a stock panel. Single DefenseLite sheets can be as large as 156 by 96 inches, and the shield can be mounted on the exterior or interior side of the glazing.

We install overglaze polycarbonate systems such as DefenseLite and BulletShield (manufactured by Impact Security, LLC); our DefenseLite and BulletShield page describes the offering. If you are still deciding which kind of product an opening needs, start with our security window film page. This post goes deeper on the overglaze itself.

How It Attaches

How it attaches, and why the air gap is vented

The manufacturer says the panels are "mounted to your existing glazing frames using a custom vented aluminum extrusion that creates stand-off from your primary window and door glass." The parts it names include UV-coated polycarbonate shields, aluminum extrusions, structural adhesive, VHB tape and security-tipped anchors, with custom powder-coating to match the existing frames.

The attachment is only as good as what it attaches to. The manufacturer's own retrofit guidance says: "If the primary glazing frame is corroded, loose, or poorly attached, it may need repair before adding a stronger shield." Someone should look at the real frame before anyone quotes a result, which is the discipline in our post on what to ask a window film installer.

The space between the shield and the original glass is deliberately not sealed. The manufacturer says "it is not advisable to hermetically seal the air space between over-glazing and the prime window," and describes a problem it calls pillowing, where heat makes plastic glazing expand and bow. Its answer is the vented extrusion. That is the manufacturer's engineering rationale; we did not find an independent study of it, so we present it as theirs. The movement itself is ordinary physics: Plaskolite, a polycarbonate sheet maker, says its sheets "expand with heat and contract with cold" and advises allowing 1/16 inch per foot of length and width. That is a generic guideline, not a statement about any one shield, but it shows why the installation detail matters.

Forced Entry

What the forced-entry tests measure, and what one real report shows

Most published overglaze strength claims come from the manufacturer. Its product page says "250 times stronger than glass," and its blog gives a range of "approximately 200 to 250 times." The manufacturer states these figures; neither page names a test method, glass type or thickness. We do not treat the number as a rating, and you should not accept it as one in a specification.

The one independent document we found is an Intertek test report on a DefenseLite PRO specimen, tested to ASTM F1233 in March 2022 at Intertek's York, Pennsylvania lab. The manufacturer publishes it as a PDF. What it says:

The result. "The test specimen achieved a Forced Entry Class of 1.4 (Contraband) and 2.2 (Body Passage)."
How it ended. A 1/8-inch rod passed through the specimen 2 minutes 46 seconds into the propane-torch sequence. An 8 by 8 by 5 inch solid cube passed through after two sledge-hammer impacts, and testing stopped. The specimen held for a time and was eventually defeated.
The specimen. 29.75 by 29.75 inches, a nominal 0.375 inch thick, and "rigidly mounted." A small lab sample, not a storefront.
The lab's own limits. The report "does not constitute certification of this product," and its results "are relevant only to the sample(s) tested."

That is useful evidence that a polycarbonate shield takes real effort to get through. It is not evidence of how a particular installed system will perform. F1233 is also a time-and-tools method; a U.S. Army Corps of Engineers guide specification describing it says power tools, or devices needing more than two people to operate, are specifically exempted. We did not obtain the standard itself, so we will not convert class numbers into minutes of attack. For the general idea that delay only helps if someone responds, see our post on whether security film stops break-ins.

Ballistic Ratings

Reading UL 752 without the folklore

BulletShield is the manufacturer's ballistic line. Its page says BulletShield "has been independently tested to UL752 standards" and that "all ballistic test reports are available for review." It also says systems may use plastics, polycarbonates or glass-clad shields depending on requirements, and its own articles describe the maximum level differently. That is exactly why you ask for the report for the configuration proposed, not the headline.

The numbers were replaced. UL says the 11th edition of UL 752 uses Performance Levels 1 through 10, while the latest 12th edition uses designations: UL-HG for handguns, UL-RF for rifles and UL-SG for shotguns, with letters. UL-HG-A is a 9 mm Luger FMJ RN, 124 grain round; UL-HG-B is a .357 Magnum; UL-HG-C is a .44 Magnum. UL's tables carry the note: "There is no hierarchy of threat severity in this list." The letters name a threat; they are not a ladder. Older numbering is still common, including on Impact Security's pages and in school documents (see our post on security film for schools and districts).

A higher number did not always mean a bigger gun. On the older scale, as the manufacturer transcribes it, Level 1 is three shots of 9 mm, Level 2 three of .357 Magnum, Level 3 three of .44 Magnum, and Level 6 goes back to 9 mm with five shots. So ask: which edition, which round, how many shots?

Ratings are small-sample and voluntary. UL says manufacturers submit samples "typically 12 inches by 12 inches," that compliance is voluntary, and that code authorities typically treat the UL label as proof of compliance. A handgun rating does not cover a rifle round; the manufacturer says so itself. We use the term bullet-resistant, which is what a tested, rated system can honestly claim.

ASTM F3561 is not a ballistic rating. It simulates an active shooter weakening a specimen with rounds such as 5.56 NATO, then applies a pendulum impact that steps from 50 to 400 foot-pounds across its levels. The standard says it "is not to be used for ballistic resistant glazing rating," that projectiles may pass through, and that it is a laboratory test on full systems, "not applicable for field testing." The manufacturer states F3561 results for some products, but we have not seen an F3561 report for any DefenseLite configuration, so we do not quote them.

The Limits

What a rating does not tell you

Every number above comes from a lab with a specimen in a test frame. A building has a real frame, real anchors and a real wall behind them. The manufacturer's own words: "the overall security of the opening is only as strong as its weakest component." Does the report cover the same shield, extrusion, attachment and size proposed for your opening? If not exactly, it is a useful reference and not a statement about your opening.

That is also where an honest installer will sometimes say an overglaze is the wrong answer. Blast hazards are a different standard family; our post on writing a blast film specification shows the same test-report discipline.

Care and Service Life

Care and service life: scratches, cleaning, thermal movement

Polycarbonate scratches. The manufacturer describes DefenseLite sheets as UV capped, with a sacrificial surface film it says defeats graffiti tagging. An Impact Security article advises mild soap, water and non-abrasive cloths, and avoiding ammonia-heavy cleaners, abrasive pads, razor blades and harsh solvents, plus periodic inspection of anchors, seals and panel clarity. Plaskolite's care guide for its own sheet adds that deep scratches from sharp objects cannot be repaired. The exact grade and coating of any DefenseLite shield is not published on the pages we reviewed, so ask for a care sheet for the installed system.

Because there is an extra panel and air space in front of the original glass, it is also fair to ask whether that has been considered for your glass type, especially insulated glass. We are not claiming a problem; we are saying ask. See our post on dual-pane glass and thermal stress.

Code Questions

Egress, fire and building-code questions to ask before anyone drills a hole

We are not code officials, and we found no source saying how code treats a field-applied polycarbonate overglaze. Here are questions a building official may ask, with actual code text where it exists.

Can anyone still get out? The manufacturer says an overglaze "must not block emergency exits, required ventilation, door swing, panic hardware, fire-rated assemblies, or required openings." For homes, the 2022 California Residential Code, R310.4.4, says that where "bars, grilles, covers, screens or similar devices" are placed over emergency escape and rescue openings, they "shall be releasable or removable from the inside without the use of a key or tool or force greater than that required for the normal operation of the escape and rescue opening." Whether an overglaze counts as one of those devices is for your building official to say. We confirmed the text only for the 2022 edition.

Is the plastic acceptable? Chapter 26 of the California Building Code covers light-transmitting plastic: technical data to substantiate its use (2606.2), identification (2606.3) and ignition and burning limits (2606.4). Whether it applies to a field-applied overglaze, we could not confirm. Ask the official, and ask the manufacturer for fire-classification paperwork on the actual shield; we did not find any published.

Does it change the glass behind it? Our post on whether window film is safety glass covers safety glazing marks. For an overglaze we found no source on whether it changes an opening's safety-glazing status, so do not assume it does.

Choosing

Film, overglaze or replacement: decide opening by opening

One building rarely needs one answer. Frame condition, egress, threat and how long a delay would matter differ door by door. Our three-way comparison is the place to start, including the cases where film or an overglaze is the wrong recommendation.

What to Ask For

What to ask for in writing

The test report for the exact configuration proposed: shield, extrusion, attachment, size and standard edition, not a brochure.
The right standard named correctly: UL 752 designations versus older levels; F1233 versus F3561.
Install position for each opening, exterior or interior.
A frame and anchor assessment, and what was repaired first.
A written code review covering egress, required openings and any material approval.
Warranty and care paperwork. The manufacturer's own documents differ, so get the terms for your system in writing.

If you would like us to look at your openings, contact us and we will tell you what we think the evidence supports for each one.

Questions

Overglaze polycarbonate retrofit — FAQ.

Is an overglaze the same thing as security film?

No. Film is applied to the glass. DefenseLite is a polycarbonate shield mounted on its own aluminum extrusion to the existing frame, with an air space between the shield and the original glass. The manufacturer says it does not replace or remove the existing glass, frames, gaskets or hardware.

Can anyone still get through a window with an overglaze on it?

Yes, given enough time and tools, and no source we found says otherwise. In the one independent forced-entry report we found, a 29.75-inch DefenseLite PRO specimen reached ASTM F1233 Class 1.4 (contraband) and 2.2 (body passage), and was then defeated: a rod passed through during the propane-torch sequence, and a test block passed through after two sledge-hammer impacts. The manufacturer itself says all security glass solutions can be broken if numerous, repeated attempts are made.

What does UL 752 Level 1 mean?

On the older numbered scale, Level 1 is three shots of 9 mm. UL's current 12th edition replaced numbered levels with designations such as UL-HG-A (9 mm Luger FMJ RN, 124 grain) and notes that its list has no hierarchy of threat severity. The ratings come from laboratory tests on small samples, typically 12 by 12 inches.

Is the manufacturer's 250 times stronger than glass figure a rating?

No. It is a manufacturer statement. The product page gives no test method, glass type or thickness, and the manufacturer's own blog gives a range of 200 to 250 times.

What should I check before an overglaze is installed?

Check the condition of the existing frame, because the manufacturer says a corroded or loose frame may need repair first. Check egress and required openings, ask for the test report for the exact configuration being proposed, ask your building official whether any material approval is needed for light-transmitting plastic, and get the warranty paperwork in writing, because the manufacturer's own documents differ.

Sources

Where these findings came from.

Intertek Building & Construction. Performance Test Report, ASTM F1233 Testing on DefenseLite PRO, Report N2788.01.01-119-12 R0, March 2022. Full report (PDF, manufacturer-hosted).
ASTM International. F3561-22, Standard Test Method for Forced-Entry-Resistance of Fenestration Systems After Simulated Active Shooter Attack. Licensed copy hosted by the State of Tennessee (PDF).
UL Solutions. Testing and Certification for Bullet-Resistant Materials (UL 752). ul.com.
UL Solutions. What Does It Take to Stop a Speeding Bullet? ul.com.
Impact Security, LLC. DefenseLite product page and BulletShield product page. Manufacturer statements, attributed as such in this post.
Impact Security, LLC. Retrofit security glazing article and ballistic standards page.
Plaskolite. TUFFAK Polycarbonate Sheet FAQs, MSC123 0818. Generic polycarbonate sheet guidance, not specific to DefenseLite.
U.S. Army Corps of Engineers. UFGS 08 34 01, security glazing guide specification. WBDG (PDF).
2022 California Residential Code, R310.4.4, and 2025 California Building Code, Chapter 26, as reproduced on UpCodes. Confirm current text with your building official.

Keep Reading

DefenseLite and BulletShield

What our overglaze polycarbonate retrofit offering covers, and where it fits next to film.

See the retrofit systems →

Security film vs. laminated glass vs. replacement

How to decide opening by opening, including the cases where film or an overglaze is the wrong recommendation.

Read the comparison →

Does security window film stop break-ins?

The break-in sequence, the idea of delay, and where film ends and an overglaze begins.

Read the answer →

Weighing an overglaze for your openings?

We'll look at your frames, your glass and your concerns, tell you honestly what the test evidence does and does not support, and put the findings in writing before anything is drilled or installed.

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