3151 Market Street Philadelphia PA
Architects, façade consultants, and glaziers are pushing glass farther than ever—larger units, tighter thermal targets, and more demanding owners. Yet one of the most critical parts of an insulating glass unit (IGU) often gets the least design attention: the spacer at the edge of the glass.
Viracon’s Viracon Thermal Spacer (VTS®) is a proprietary warm-edge spacer engineered to improve thermal performance, durability, and aesthetics, especially on large-format IGUs. In this MCO Insights piece, we break down what VTS is, why it matters, and where it can give your next façade an advantage.
Why the Edge of Glass Deserves More Attention
When you’re evaluating glass performance, center-of-glass values tell only part of the story. At the perimeter, traditional metal box spacers (aluminum or stainless) can create a thermal weak point:
- Lower edge-of-glass U-values
- Increased risk of condensation at the frame line
- Colder interior surfaces where people sit, walk, and work
A warm-edge spacer is designed to soften that weak spot, improving thermal continuity around the IGU. That translates into:
- More comfortable interior conditions near the façade
- Better condensation resistance
- A more robust envelope when you’re chasing tight energy targets
Viracon developed VTS® specifically to address those edge-of-glass challenges.
What is Viracon Thermal Spacer (VTS®)?
VTS® is a single-component thermoplastic spacer that replaces several traditional components at the edge of the IGU:
- Replaces:
- Metal box spacer
- Separate desiccant
- Separate PIB primary seal
- Integrates:
- Thermoplastic body (the spacer)
- Integrated desiccant
- Integrated polyisobutylene (PIB) as primary seal
The spacer is chemically bonded directly to:
- The glass lites, and
- The proven secondary silicone sealant
That chemical bond eliminates the need for additional vapor barriers, acrylic adhesives, or extra PIB tapes. The result is a simpler, more robust edge construction designed for long-term seal integrity.
Key Performance Benefits of VTS®
1. Superior Seal Integrity
- Chemical bond to glass and secondary silicone
- Increased stability across hot and cold climates
- Reduced reliance on thin PIB lines that can stretch or thin under temperature cycling
- Supported by a Special 12-Year Limited Warranty for VTS® units
As IGUs expand and contract with daily temperature swings, the thicker VTS band experiences much lower strain than a traditional thin PIB bead. That contributes to better argon retention and long-term seal performance.
2. Warm-Edge Thermal Performance
- Warm-edge spacer design paired with argon fill as standard
- Improves edge-of-glass U-value:
- ~14.4% better than aluminum spacers
- ~7% better than stainless steel spacers
- Argon retention improved by ~35% compared to box spacers
- Contributes to higher condensation resistance (CR) values
For designers, that means a perimeter that behaves more like the center of glass—helping you close the gap between modeled performance and real-world comfort.
3. Cleaner, Monolithic Aesthetics
- Smooth, matte black extrusion at the edge
- Robotically extruded for a consistent sightline and setback
- Coating edge deletion occurs within the VTS footprint, reducing visual clutter
- Eliminates typical metal spacer “tells”:
- Shine and reflectivity
- Perforations
- Visible metal connection splices
From a design standpoint, VTS produces a dark, uniform perimeter line that supports a clean, contemporary aesthetic at the frame.
Big Glass, Big Advantage: VTS® Size Capabilities
As projects move toward larger and more transparent façades, spacer limits become critical. VTS is specifically engineered for large-format IGUs:
- Minimum IGU size with VTS: 14" x 20"
- (Not available in 12" x 12" or 5" x 7" units; cutout samples are used instead.)
- Maximum size: approximately 129-13/16" x 236"
- Weight limit: up to 3,000 lbs per IGU
On very large units, VTS isn’t just an option—it becomes a requirement:
- For IGUs larger than 120" x 204", VTS must be used.
VTS is also capable on non-rectangular shapes with angles greater than 30°, giving designers flexibility for more complex geometries while maintaining performance.
Tested to Industry Standards – and Beyond
VTS has been validated through industry-recognized tests used for IGU certification and durability evaluation:
- ASTM E2188/E2190 – Temperature and humidity cycling (required for IGCC certification)
- ASTM G155 – UV stability
- ASTM E1233 – Wind and structural strength
- ASTM E2189 – Volatile fog resistance
Viracon also subjected VTS to extended UV and accelerated weathering cycles:
- Repeating cycle of:
- 4 hours of UV and visible light at 70°C and 50% RH, followed by
- 30 minutes dark cycle at 40°C and 80% RH
- Over a 32-week exposure period
- No degradation of VTS observed in vision or spandrel cavities
Additional thermal exposure tests approximating spandrel temperatures also showed no degradation. For project teams, that testing history is a key part of the story when owners ask about long-term durability.
How VTS® is Applied: Robotic Edge Precision
The VTS spacer is applied in-factory via robotic extrusion:
- The robot applies a continuous bead of thermoplastic spacer around the perimeter of the first glass lite.
- The bead is positioned inboard of the glass edge according to project-specific sightline requirements.
- The start and end of the bead overlap, creating a splice zone typically about 6 inches long.
- That splice is pressed to fuse the start and end of the spacer bead.
- The second lite is placed to form the hermetically sealed IGU.
This robotic process helps ensure:
- Consistent sightline from unit to unit
- Uniform spacer thickness and position
- Repeatable, inspectable edge construction at scale
The VTS® Splice: Controlled, Inspected, and Expected
Because VTS is robotically extruded, each unit includes a single splice where the bead starts and finishes. Rather than being a defect, this is an inherent, controlled feature of the system.
To manage and verify splice quality, Viracon uses AI-based visual inspection:
- A Cognex camera on the line captures an image of each splice.
- The system compares it to a trained reference image of a “good” splice.
- If the splice falls outside acceptable parameters, the line automatically shuts down and the affected IGU is removed for review.
For architects and consultants, that level of automation and QC helps reduce the risk of edge irregularities and ensures consistent execution of the design intent.
VIN: Viracon Identification Number – Traceability Built In
An additional benefit available only with VTS® is the Viracon Identification Number (VIN):
- A 24-digit code laser-printed discreetly on the spacer.
- The first 8 digits are unique and encode:
- Glass thickness
- Size
- Substrate
- Heat treatment
- Manufacture date, and more
For owners, facility teams, and consultants, VIN enables:
- Faster identification and replacement of specific units
- Better asset management for large campuses and complex buildings
- Clearer documentation when reviewing performance, maintenance, or warranty issues
In practical terms, VIN means you’re not guessing which glass is in an opening years later—you can read it directly from the spacer.
Where VTS® Adds the Most Value
While VTS can be used across a wide range of projects, it offers outsized benefits in a few specific scenarios:
- Large-format IGUs and tall façades
- Any units > 120" x 204" (VTS is required here)
- Long-span lobby walls, atria, feature façades
- High-performance envelopes
- Projects with aggressive U-value and condensation resistance targets
- Cold and mixed climates where edge performance drives occupant comfort
- Signature and image-critical projects
- Headquarters, hospitals, universities, cultural venues
- Projects where long-term aesthetics and owner perception are high priorities
- Owners focused on lifecycle and operations
- Campuses, healthcare, and institutional owners who value traceability, maintenance, and predictable performance
Bringing It All Together
Viracon Thermal Spacer (VTS®) rethinks one of the most critical but often overlooked parts of the IGU:
- It’s a single-component warm-edge spacer with integrated desiccant and PIB.
- It’s chemically bonded to glass and secondary silicone for superior seal integrity.
- It improves edge-of-glass thermal performance, argon retention, and condensation resistance.
- It enables very large IGU sizes with a controlled, AI-inspected splice.
- It offers VIN-based traceability only available with VTS®.
For architects, consultants, and glaziers, VTS is a way to back up your envelope design intent—thermally, visually, and operationally—right at the edge where it matters most.
If you’d like help reviewing where VTS could support your next façade, Martineau & Co can walk through your elevations, IGU sizes, and performance targets and identify where VTS provides the most value.
