Infrared Transmission Glass (Thermal Barriers)
Infrared-transmitting glazing must be selected for a defined wavelength band and verified as a complete assembly. A claim that glass is “IR transparent” does not establish its thermal efficiency, safety, or fire rating. Before ordering, confirm the spectral-transmission data, code requirements, frame details, and certifications for the exact glass, coatings, interlayers, seals, and installation.
If you are specifying glazing for a sensor, imaging system, or other infrared use, the key question is not simply whether a pane passes infrared light. It is whether the installed assembly transmits the wavelengths your equipment needs while meeting the building’s energy, safety, and fire requirements. Treating those as separate checks can prevent a costly mismatch.
I start by defining the intended wavelength band and collecting product-specific evidence. Then I check the opening, frame, code conditions, and installation details. This guide follows that sequence. “Thermal barrier” can mean a building-code protection layer for foam plastic, not a promise that glazing provides good insulation; the distinction matters throughout the specification.
Planning: Define the Infrared Band and Code Performance
The first step is to state the wavelengths the system must receive, in micrometres (μm). For common longwave thermal imaging, the relevant band may be 8–14 μm, but the equipment’s needs govern. Request a spectral-transmission curve for the complete assembly, and assess thermal, safety, and fire performance separately.
Ask for spectral data, not a broad claim
A spectral-transmission curve shows how much radiation passes through a product at different wavelengths. Ask for data covering the entire band your equipment uses, along with the test method and the exact build-up tested. A curve for a single sheet may not describe a coated, laminated, or insulated unit.
Ordinary architectural glass is generally not transparent to longwave thermal-imaging radiation. A pane that looks clear to the eye may block much of the 8–14 μm signal. Conversely, a material that transmits the desired infrared band is not automatically suitable for an occupied opening.
Confirm energy performance independently
Use the whole-product NFRC 100 U-factor to assess heat flow through the rated product. A lower U-factor indicates less heat flow under the rating conditions. Use NFRC 200 data for solar heat gain coefficient (SHGC) and visible transmittance. SHGC is the fraction of solar heat that enters; visible transmittance describes visible light passing through.
Neither measure tells you how well the glazing transmits a specific infrared band. Code limits depend on the adopted energy code, climate zone, and assembly type. Ask the project’s code professional to confirm the applicable limits rather than relying on a generic target.
| Requirement | Evidence to request | What it establishes |
|---|---|---|
| Infrared transmission | Spectral-transmission curve across the required band | Wavelength-specific performance for the tested build-up |
| Thermal performance | NFRC 100 whole-product U-factor | Rated heat flow through the product |
| Solar and visible performance | NFRC 200 SHGC and visible transmittance | Rated solar heat gain and visible light transmission |
| Safety | Applicable certification and permanent marking | Compliance with the required safety-glazing standard |
| Insulating-glass unit | ASTM E2190 documentation, where applicable | Evidence for insulating-glass durability requirements |
Planning takeaway: Put the wavelength band and required supporting documents in the specification before comparing products.
Access and Clearances: Confirm Opening, Frame, and Safety Conditions
Before choosing a glass build-up, record the opening size and use, exposure, climate zone, fire requirements, and any hazardous-glazing conditions. Then check the frame and support details with the glass and glazing-system manufacturers. These checks help confirm that the proposed assembly can fit, move, drain, and meet the project’s required ratings.
Survey the opening and its use
Measure the opening and document its location, exposure, and expected service conditions. Check whether people could strike the glass or whether the opening is in another location that local code treats as hazardous. Requirements vary by jurisdiction and project, so confirm them with the authority having jurisdiction or the project code professional.
Where glazing is in a code-defined hazardous location, use permanently marked glazing certified to the applicable CPSC 16 CFR Part 1201 category or ANSI Z97.1 class required by the jurisdiction. Do not assume that an infrared-transmitting material has this certification. Ask for evidence tied to the specified product.
Check the frame and assembly details
A frame must support the proposed glass weight and accommodate movement. Confirm the approved glass thickness and make-up, edge support, setting blocks, spacer, sealant, gaskets, and clearances with the system manufacturer. Also check drainage and perimeter details where the system requires them.
Changes to any of these parts can affect the performance of the installed assembly. A coating, interlayer, seal, or spacer may alter the infrared transmission from that shown for a basic glass sample. Ask the manufacturer to confirm that the complete build-up retains the required spectral performance.
For sealed insulating-glass units, request compliance documentation to ASTM E2190, where applicable, and confirm that fabrication uses the applicable ASTM C1036 or ASTM C1048 glass specification. Verify that the chosen coatings, interlayers, and edge seals are compatible with the intended infrared band. These documents address different parts of the assembly; they do not replace spectral-transmission data.
Access takeaway: Resolve opening, frame, safety, and fire conditions before approving the glass make-up.
Execution: Specify, Procure, and Install the Tested Assembly
Specify and order the same complete assembly for which the manufacturer supplies performance evidence. Include the glass layers, coatings, interlayers, cavity, seals, frame, and required certifications in the submittal review. Installation should follow the approved system details; field changes can make test data or listings no longer apply.
Write a complete specification
Identify the required infrared band in μm and request a spectral-transmission curve for the proposed complete assembly. Name the required NFRC data, safety-glazing certification, fire documentation, and insulating-glass documents where they apply. Include the intended opening, frame, and relevant project conditions so the manufacturer can check the proposed configuration.
Use clear submittal questions:
- Does the spectral curve cover the full required wavelength band?
- Does it represent the specified glass and the complete installed build-up?
- Are the NFRC values for the whole product, not just one pane?
- Is the safety-glazing evidence for the exact product and required category or class?
- Do fire or foam-plastic requirements apply to this location?
- Are the frame, edge support, sealant, spacer, and installation details approved?
Do not accept “IR-transmitting” as a substitute for these answers. A marketing description does not prove a particular wavelength range, U-factor, safety rating, or fire rating.
Coordinate the thermal-barrier requirement
In building codes, a thermal barrier can refer to protection for foam plastic, rather than the insulating function of a window. Where foam plastic is present, the adopted code’s provisions apply independently of the glazing. For example, IRC R316.4 requires a 15-minute thermal barrier except where a listed exception applies. Confirm the adopted code edition, applicable exceptions, and assembly listing with the project code professional.
Do not replace or remove a required thermal barrier based on the presence of specialty glazing. Glazing’s infrared transmission does not establish compliance with foam-plastic protection rules. Resolve the fire-protection design and any required listing before procurement.
Install without unapproved changes
Procure the complete tested assembly and install it using the manufacturer’s instructions and approved project details. Do not field-cut, coat, laminate, or substitute components unless the manufacturer confirms that the change preserves the required performance and listing. If a substitution becomes necessary, obtain revised documentation before installation.
Execution takeaway: The performance evidence must match what arrives at the site and what the installer puts in the opening.
Real-World Installation Case Studies: Apply the Checks to Typical Scenarios
The examples below are illustrative design scenarios, not reports of specific completed projects. They show how the same review sequence can reveal different risks. In each case, the right next step is to compare the proposed complete assembly with the equipment band and the project’s code requirements.
| Scenario | Main risk | Useful check before approval |
|---|---|---|
| Sensor behind a clear-looking exterior pane | The pane may block the needed longwave signal | Request a curve covering the sensor’s full band for the complete build-up |
| Occupied opening with specialty glazing | Infrared performance may be mistaken for safety compliance | Confirm the required permanent marking and certification |
| Insulating-glass unit with coatings | Coatings or seals may change transmission | Review full-assembly spectral data and relevant unit documentation |
| Foam plastic near an opening | Glazing may be treated as a replacement for a required thermal barrier | Check the adopted code, exceptions, and assembly listing |
In a sensor-opening review, I would first match the equipment’s stated band to the curve. If a supplier provides only a general claim or data for one sheet, I would not treat that as proof for a coated insulating unit. The next step is to request data for the proposed assembly or ask the manufacturer to confirm the configuration in writing.
For an occupied opening, I would then check whether the location triggers safety-glazing rules. The infrared specification and the safety certification answer different questions, so both need their own evidence. If foam plastic is also present, the code review must address its thermal-barrier protection separately.
Case-study takeaway: A product can pass one check and fail another. Keep spectral, energy, safety, and fire reviews distinct.
Verification: Document Spectral, Thermal, and Safety Compliance
At delivery and after installation, compare the installed product with the approved submittal. Check labels, glass make-up, frame details, and installation features, then retain the supporting records. This closeout step creates a clear link between the intended infrared performance and the assembly that was actually installed.
Inspect and retain project records
Review product labels and markings against the approved documents. Check setting blocks, gaskets, seals, drainage, and perimeter continuity against the manufacturer’s approved details. If the product or configuration differs from the submittal, pause acceptance and obtain written confirmation that the change remains compliant.
Keep a project file with:
- The spectral-transmission curve for the installed configuration
- NFRC 100 U-factor and NFRC 200 SHGC and visible-transmittance data
- Safety-glazing certification and marking evidence
- ASTM E2190 documentation and applicable glass specifications, where relevant
- Fire, foam-plastic, and assembly-listing documents, where required
- Approved shop drawings, installation details, and any manufacturer-approved changes
These records help future reviewers distinguish tested performance from assumptions based on appearance or a short product description.
Verification takeaway: Close out against the actual assembly, not a product name or sample alone.
Conclusion: Approve the Assembly, Not Just the Glass
A sound specification starts with a defined infrared band and ends with evidence for the installed assembly. Spectral transmission, thermal performance, safety glazing, and fire protection are separate requirements; none can be inferred from the others. Confirm the adopted code and manufacturer approvals before ordering or changing components.
Use a simple approval rule: if the data do not match the proposed build-up, or a required rating is missing, do not assume the assembly will perform as intended. Ask for the missing evidence and resolve the issue before installation.
FAQ: Infrared-Transmitting Glazing and Thermal Barriers
These answers address common specification questions. The central distinction is that wavelength-specific transmission, energy performance, safety, and fire protection are measured or governed in different ways. Confirm local code requirements and the exact tested configuration for each project.
What does infrared-transmitting glass mean?
It means a glazing material or assembly allows some infrared radiation to pass through within a stated wavelength range. The term alone does not state how much passes, which wavelengths pass, or whether the product meets energy, safety, or fire requirements. Request a spectral-transmission curve for the complete assembly.
Does clear glass transmit thermal-imaging radiation?
Not necessarily. Ordinary architectural glass is generally not transparent to longwave thermal-imaging radiation, including the commonly used 8–14 μm band. Visual clarity does not prove infrared transmission. Check data for the exact glass build-up and the wavelengths required by the imaging equipment.
What wavelength range should I specify?
Specify the range required by the equipment, in micrometres. For common longwave thermal imaging, 8–14 μm is an example, not a universal requirement. Confirm the system’s operating band and measurement needs with its manufacturer, then request spectral data that covers that full range.
Does infrared transmission show that the glass is energy efficient?
No. Infrared transmission does not establish a product’s U-factor or SHGC. Request the whole-product NFRC 100 U-factor and NFRC 200 SHGC and visible-transmittance data. The applicable energy-code limits depend on the adopted code, climate zone, and assembly type.
Is infrared-transmitting glass automatically safety glazing?
No. If the location is hazardous under the applicable code, the glazing must meet the required safety-glazing rules. Confirm permanent marking and certification to the applicable CPSC 16 CFR Part 1201 category or ANSI Z97.1 class required by the jurisdiction.
What does ASTM E2190 cover in this specification?
ASTM E2190 documentation is relevant to sealed insulating-glass units. It does not replace spectral-transmission data, safety-glazing evidence, or energy ratings. Confirm that the documentation applies to the proposed unit and that its coatings, interlayers, and edge seals preserve the required infrared band.
Can a thermal barrier mean something other than window insulation?
Yes. In code discussions involving foam plastic, a thermal barrier can mean a protective layer required by the adopted building code. For example, IRC R316.4 requires a 15-minute thermal barrier except where a listed exception applies. Confirm the local code edition and assembly requirements.
Can I change a coating or laminate in the field?
Do not field-coat, laminate, cut, or substitute components unless the manufacturer confirms that the change preserves the required performance and any applicable listing. A modification can make the available test data or approval no longer apply to the installed assembly.
(This article was written by one of our staff writers, Steven Langford. Visit our Meet the Team page.)
