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Heat soaked glass (HST) manufactured to EN 14179, reducing spontaneous breakage to less than 0.1%. Ideal for high-rise facades, skylights, atria and public buildings where glass replacement is costly. Max size 3300×20000mm, thickness 5–25mm. CE / ASTM C1048 / AS-NZS 2208 / EN 14179 certified.
Engineered Reliability for High‑Rise Facades, Skylights & Public Buildings
Spontaneous Breakage Rate < 0.1% — The Reliability Upgrade for Architectural Tempered Glass
Heat soaked glass (also referred to as HST glass or heat‑soak‑tested tempered glass) is fully tempered glass that has undergone an additional thermal conditioning cycle after tempering. The panels are placed in a heat‑soak oven, gradually heated to approximately 280–300°C, held at temperature for at least 2 hours, and then slowly cooled. During this process, tempered glass containing unstable nickel sulfide (NiS) inclusions will break inside the oven rather than months or years later on the building façade.
For architects, façade contractors, and building owners, the consequence is decisive: the spontaneous breakage rate is reduced to less than 0.1% — roughly one tenth of the risk associated with standard tempered glass. For projects where replacing a glass panel means closing a high‑rise floor, dismantling a curtain wall, or cordoning off a public space, heat soaking transforms an unpredictable liability into a controlled, documented process.
| Key Specification | Value |
|---|---|
| Glass Type | Fully tempered + heat soak tested (HST) |
| Thickness Range | 5mm – 25mm |
| Maximum Size | 3300 × 20000 mm (flat) |
| Heat Soak Process | Per EN 14179: heat to ~280–300°C, hold ≥ 2 hours |
| Residual Spontaneous Breakage | < 0.1% (target; EN 14179 limit ≈ 1 break per 400 tons) |
| Surface Compressive Stress | ≥ 95 MPa (tempered property retained) |
| Applicable Standards | EN 14179, EN 12150, ASTM C1048, AS/NZS 2208, CCC |
| Quality System | ISO 9001 |
| HST Documentation | Batch‑level heat‑soak records available per project |
| MOQ | 100 m² |
| Lead Time | 15–25 days (incl. heat soak cycle) |
Tempered glass derives its strength from a surface compressive stress layer. However, microscopic nickel sulfide (NiS) particles — inevitable trace impurities in float glass — can become trapped in an unstable α‑phase during tempering. At ambient building temperatures, these particles slowly convert to the β‑phase, expanding by ~4% and generating internal stress. When that stress exceeds the glass strength, the panel shatters spontaneously, with no external trigger.
Industry data shows that untreated tempered glass carries a typical spontaneous breakage rate of 0.1%–0.3%. Heat soaking accelerates the NiS phase transformation under controlled conditions: defective panels fail in the oven, and only "clean" panels ship to site.
💡 Key fact for specifiers: Heat soaking does not make the glass stronger — it makes the population of installed glass reliable. The tempering strength (4–5× annealed) is unchanged; the uncertainty is removed.
| Property | Standard Tempered | Heat Soaked Glass (HST) |
|---|---|---|
| Manufacturing steps | Cut → Edge → Temper | Cut → Edge → Temper → Heat Soak |
| Spontaneous breakage rate | 0.1% – 0.3% | < 0.1% (typical 0.01%–0.03% in practice) |
| Mechanical strength | 4–5× annealed | 4–5× annealed (unchanged) |
| Fragmentation safety | Granular | Granular (unchanged) |
| Process time | Baseline | +24–48 hours for heat soak cycle |
| Cost premium | – | Moderate (see pricing) |
| Best for | General applications | High‑rise façades, skylights, public buildings |
| EN 14179 compliance | No | Yes |
On towers above 8–10 floors, replacing a spontaneously broken panel requires suspended scaffolding or rope access, often costing thousands of dollars per panel. Specifying HST glass reduces this risk to < 0.1%, protecting both budget and reputation.
Overhead glass failure is a direct safety hazard. Heat soaked tempered glass — often further laminated — is the default specification for skylights in airports, shopping malls, and hotel atriums.
Airports, train stations, stadiums, and government buildings carry high foot traffic and high liability exposure. HST glass is routinely mandated by project consultants for these applications.
The larger the panel, the higher the absolute risk. For jumbo panels up to 3300 × 20000 mm, heat soaking is strongly recommended — a single failure on a 60 m² panel is both spectacular and expensive.
Where glass carries live loads and human safety depends on integrity, HST (usually combined with lamination) provides the reliability baseline.
Structural silicone‑glazed assemblies leave no margin for replacement. HST glass minimizes the risk of a panel blowing out years after installation.
Combined with laminated construction, HST glass forms the backbone of hurricane‑resistant curtain walls.
| Parameter | Specification |
|---|---|
| Glass Substrate | Clear, Low‑Iron, Tinted (bronze/grey/blue/green), Coated |
| Thickness | 5mm, 6mm, 8mm, 10mm, 12mm, 15mm, 19mm, 22mm, 25mm |
| Maximum Size (flat) | 3300 × 20000 mm |
| Minimum Size | 300 × 300 mm |
| Surface Compressive Stress | ≥ 95 MPa (per EN 12150) |
| Fragmentation | ≥ 40 fragments in 50×50 mm (per EN 12150) |
| Heat Soak Temperature | 280–300°C (process per EN 14179) |
| Holding Time | ≥ 2 hours at peak temperature |
| Residual Breakage Rate | < 0.1% (EN 14179 limit: 1 break per 400 tons) |
| Light Transmittance (clear 12mm) | ≥ 90% |
| Solar Heat Gain (coated options) | SHGC 0.23–0.45 available |
| Edgework | Flat polish, pencil edge, beveled, seamed |
| Further Processing | Lamination, IGU, Low‑E coating, ceramic frit, digital printing |
| Standards | EN 14179, EN 12150, ASTM C1048, AS/NZS 2208, CCC, ISO 9001 |
| HST Documentation | Batch‑level temperature‑time charts & QC reports |
Every heat soaked glass panel from JUMBO Glass Group passes through a documented, auditable process:
📌 HST records and QC documentation can be provided per production batch to support project certification and owner acceptance.
Heat soaking adds a moderate premium over standard tempered glass, driven by oven occupancy time and energy. Indicative FOB pricing:
| Thickness | Standard Tempered (USD/m²) | + Heat Soak Upgrade (USD/m²) |
|---|---|---|
| 6mm | 9–14 | +3–5 |
| 8mm | 12–18 | +3–5 |
| 10mm | 13–23 | +4–6 |
| 12mm | 15–25 | +4–6 |
| 15mm | 18–30 | +5–8 |
| 19mm | 25–40 | +6–10 |
| 22mm | 35–55 | +8–12 |
| 25mm | 40–65 | +8–12 |
💡 For jumbo panels (> 6 m²), the heat‑soak premium is typically amortized over the panel area, making HST a highly cost‑effective insurance against single‑panel replacement costs that can run 10–50× the glass value.
Q1: What exactly is heat soaked glass?
HST glass is fully tempered glass that has undergone an additional thermal cycle (heated to ~280–300°C, held ≥ 2 hours per EN 14179) to force nickel sulfide inclusions to fracture the glass inside the oven rather than after installation.
Q2: Does heat soaking make the glass stronger?
No. The tempering strength (4–5× annealed) is unchanged. Heat soaking is a risk‑control process that eliminates defect‑prone panels from the batch.
Q3: What spontaneous breakage rate can be achieved?
Properly executed heat soaking reduces the spontaneous breakage rate to < 0.1%. EN 14179 sets the residual risk limit at 1 break per 400 tons of glass. In practice, high‑quality HST glass achieves 0.01%–0.03%.
Q4: Is heat soaking a guarantee against all breakage?
No. HST addresses NiS‑induced spontaneous breakage. Impact, thermal shock, improper installation, and edge damage remain possible failure modes. Comprehensive façade safety requires correct design, handling, and installation.
Q5: Which thicknesses can be heat soaked?
We process HST glass from 5mm to 25mm. The most common façade thicknesses are 8mm, 10mm, 12mm, 15mm, and 19mm.
Q6: Can heat soaked glass be laminated or used in insulated units?
Yes. HST glass is frequently used as the substrate for PVB/SGP laminated glass and for insulated glass units (IGU). The heat soak process is completed before lamination.
Q7: What is the maximum size for heat soaked glass?
Our furnace accommodates panels up to 3300 × 20000 mm (flat). Larger formats may be possible — please inquire.
Q8: How long does production take?
Standard tempered glass: 12–18 days. With heat soaking: 15–25 days, reflecting the additional 24–48 hour HST cycle.
Q9: Can you provide HST documentation for our project?
Yes. We provide batch‑level heat‑soak temperature‑time records, fragmentation test reports, and a certificate of conformity referencing EN 14179.
Q10: Is heat soaked glass required by building codes?
Many international standards and project specifications for high‑rise façades, skylights, and public buildings require heat soak testing per EN 14179 or equivalent. Local codes vary — consult your façade consultant.
Q11: What is the cost premium for heat soaking?
Typically USD 3–12 per m² depending on thickness. Given that a single jumbo panel replacement on a high‑rise can cost hundreds of dollars in access and labor, the ROI is compelling.
Q12: Can coated or low‑iron glass be heat soaked?
Yes. Low‑iron, tinted, and even coated glass can be heat soaked. For sensitive Low‑E coatings, we recommend discussing the coating type to ensure HST temperature does not degrade performance.
Tell us your project requirements and our engineering team will respond within 48 hours with a detailed quotation.
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With over 20 years of experience and expertise in glass manufacturing and processing, we are seasoned glass specialists, ready to answer your questions and provide guidance on product selection, installation, and maintenance.
