Toughened glass — also called tempered glass or thermally pre-stressed safety glass — is float glass that has been heated to ~620–680 °C and then rapidly air-quenched to lock in surface compression. The locked-in stress makes it 4–5 times stronger than annealed glass, and when it does break it shatters into small dice-like granules instead of long sharp shards — reducing the risk of injury. It is one of the two recognised "safety glasses" (the other being laminated) under building codes worldwide.
Indian toughened glass is governed by IS 2553 (Part 1) — Safety Glass: Architectural, Building & General Uses aligned with EN 12150. Major Indian processors / brands: Saint-Gobain Securit, AIS Stronglas, Gold Plus Tough, Sejal Toughened, Glass Wall Systems, FG Glass, Glasstech India, Asahi Glass Plants, NSG Pilkington Tough.
Toughened glass is heat-treated annealed glass. The fundamental principle is: surface compression + core tension = locked-in stress field. When external load is applied, the load must first overcome the surface compression before it can put the surface into tension — which is when glass actually breaks. Because much higher loads can be sustained, the glass is "stronger".
| Type | Description | Surface Compression |
|---|---|---|
| Fully Toughened (FT) | Standard tempered safety glass | ≥ 80 MPa (EN 12150) |
| Heat-Strengthened (HS) | Slower quench — 2x annealed strength, NOT safety glass | 24–52 MPa |
| Heat-Soak Tested (HST) | FT + heat-soak to remove NiS | ≥ 80 MPa |
| Chemically Strengthened | Ion-exchange (K+ replaces Na+); thin glass < 4 mm | 500–800 MPa (top 50 µm) |
| Curved Toughened | Bent during heating, then tempered | ≥ 80 MPa |
| Tinted Toughened | Body-tinted float + tempered | ≥ 80 MPa |
| Reflective Toughened | Coated float + tempered (hard coat only) | ≥ 80 MPa |
| Low-E Toughenable | Pyrolytic (hard) low-E coating before tempering | ≥ 80 MPa |
| Ceramic Frit / Spandrel | Ceramic ink fired onto glass during tempering | ≥ 80 MPa |
| Property | Annealed Float | Toughened | Heat-Strengthened |
|---|---|---|---|
| Surface Compression | 0 MPa | 80–150 MPa | 24–52 MPa |
| Tensile Strength | 30–50 MPa | 120–200 MPa | 70–100 MPa |
| Bending Strength (charact.) | 45 MPa | 120 MPa | 70 MPa |
| Thermal Shock (ΔT) | 40 °C | 200 °C | 100 °C |
| Density | 2500 kg/m³ | 2500 kg/m³ | 2500 kg/m³ |
| Modulus of Elasticity | 70 GPa | 70 GPa | 70 GPa |
| Coefficient of Thermal Expansion | 9 x 10−6 /°C | 9 x 10−6 /°C | 9 x 10−6 /°C |
| Light Transmission (6 mm) | 87–89% | 87–89% | 87–89% |
| Hardness (Mohs) | 5.5–6.5 | 5.5–6.5 | 5.5–6.5 |
| Fragment Count (50x50 mm) | 1–2 large | ≥ 40 small dice | 5–10 large pieces |
| Sound Reduction Rw (6 mm) | 30 dB | 30 dB | 30 dB |
| Thickness | Typical Application |
|---|---|
| 4 mm | Furniture, mobile back covers, small windows |
| 5 mm | Internal partition, shower screens |
| 6 mm | Windows, partitions, shower enclosures, doors |
| 8 mm | Frameless doors, balustrades, partitions |
| 10 mm | Frameless doors, structural glazing, balustrade |
| 12 mm | Heavy structural, large frameless doors, fins |
| 15–19 mm | Floors, stair treads, structural fins, aquaria |
| Brand | Product Names | Notes |
|---|---|---|
| Saint-Gobain Glass India | SGG SECURIT, PLANITHERM ONE T | Premium — CE / BIS |
| Asahi India Glass (AIS) | AIS Stronglas, Securityglas | Pan-India network |
| Gold Plus Glass Industry | Gold Plus Tough, GP Securityglas | Roorkee & Odisha plants |
| Sejal Glass | Sejal Toughened, Sejal Heat Soak Tested | Premium architectural |
| FG Glass / FuYao | FG Tempered | Automotive + architectural |
| Glasstech India | Tempered, HST, IGU panes | Large-format jumbo |
| Sisecam / Modiguard | Modiguard Tempered | Halol plant |
| Glass Wall Systems | GWS Tempered | Facade processor |
| NSG Pilkington (imported) | Pilkington Toughened, Pyrostop | Premium imports |
| Guardian Industries | Guardian Tempered | Imported |
| Parameter | Annealed Float | Toughened | Laminated |
|---|---|---|---|
| Strength | 1x (baseline) | 4–5x | 1x × 2 plies |
| Breakage | Sharp shards (dangerous) | Small dice (safe) | Cracks but holds (safest) |
| Safety Class (IS 2553 / EN 12600) | None | Class 1C2 / 1C3 (≥ 8 mm) | Class 1B1 / 2B2 (best) |
| Drillable / Cuttable After | Yes | NO | Yes (edge sealed) |
| Spontaneous Breakage Risk | None | Possible (NiS) — HST mitigates | None |
| Distortion / Anisotropy | None | Roller wave + anisotropy | Inherits plies |
| Sound Insulation | 30 dB | 30 dB | 35–40 dB |
| UV Cut | ~25% | ~25% | ~99% (PVB) |
| Burglar / Bullet Resistance | None | Low | High (multi-ply) |
| Cost vs Annealed | 1x | 2–2.5x | 3–5x |
| Application | Picture frame, low risk | Door, shower, balustrade, partition | Overhead, skylight, fall protection |
Toughened glass has one major hazard: spontaneous breakage caused by tiny (50–200 µm) nickel sulphide inclusions in the glass. NiS exists in two phases — α (high temp) and β (low temp). The tempering process traps NiS in the α phase. Over months / years at ambient temperature it slowly transforms to β, growing 4% in volume. In the tensile core, this expansion is enough to cause crack initiation — resulting in sudden shattering with no impact.
| Thickness | Plain Toughened (Rs/sqft) | HST Toughened (Rs/sqft) |
|---|---|---|
| 5 mm | 180 – 240 | 240 – 320 |
| 6 mm | 200 – 280 | 280 – 380 |
| 8 mm | 260 – 360 | 360 – 480 |
| 10 mm | 340 – 460 | 460 – 620 |
| 12 mm | 420 – 580 | 580 – 780 |
| 15 mm | 650 – 880 | 880 – 1200 |
| 19 mm | 950 – 1350 | 1350 – 1850 |
Add Rs 50–150/sqft for ceramic frit / spandrel printing, Rs 80–200/sqft for curvature, and Rs 100–300/sqft for low-E pyrolytic coating. Installation Rs 80–200/sqft depending on system (frameless, spider, captive).
| Standard | Description |
|---|---|
| IS 2553 (Part 1) | Safety Glass — Architectural, Building & General Uses |
| IS 14900 | Transparent Float Glass — Specification (substrate) |
| IS 3548 | Code of Practice for Glazing in Buildings |
| EN 12150-1/2 | Thermally Toughened Soda Lime Silicate Safety Glass |
| EN 14179-1/2 | Heat Soaked Thermally Toughened Soda Lime Silicate Safety Glass |
| EN 12600 | Pendulum Test — Impact Classification |
| EN 1863-1/2 | Heat-Strengthened Soda Lime Silicate Glass |
| EN 13024 | Thermally Toughened Borosilicate Safety Glass |
| ANSI Z97.1 | American National Standard for Safety Glazing Materials |
| ASTM C1048 | Heat-Treated Flat Glass |
| ASTM C1422 | Standard for Chemically Strengthened Flat Glass |
| BS 6206 | Safety Glazing Materials in Buildings (UK) |
| NBC 2016 Part 6 Sec 5 | National Building Code — Glass & Glazing |
Toughened glass is the default safety glass for most Indian residential and commercial applications — doors, shower enclosures, partitions, balustrades, facades and structural glazing. For overhead and fall-protection use, always upgrade to laminated toughened. For premium thermal & acoustic comfort, choose double-glazed units with toughened panes. For privacy, combine with frosted / etched finish; for solar control, with tinted / reflective coatings.
The substrate for every toughened pane is clear float glass. For window frame systems, see UPVC windows or aluminium sliding windows.