Thermally toughened glass

Fully tempered safety glass: fb,k 120 MPa; breaks into small blunt fragments.

Cannot be cut or drilled after toughening. Nickel sulfide inclusions can cause spontaneous breakage; the heat soak test (EN 14179) reduces the risk.

Characteristic bending strength fg,k / fb,k: 120 MPa3characteristic
Modulus of elasticity E: 70 000 MPa2nominal
Density ρ: —
Coefficient of thermal expansion α: 9 ×10⁻⁶ /K2nominal · 20–300 °C
Thermal conductivity λ: 1 W/(m·K)1nominal

How we know these values · 24 values from 5 sources

Confirmed: 2
Corroborated: 6
Single source: 16
Disagreements explained: 8

Click any value under “All values” to see the sources that state it, with dates.
8 disagreements between sources, each explained under its value.
How we rate evidence

What to watch

Sources disagree on modulus of elasticity, coefficient of thermal expansion, thermal conductivity; the reason is given under the value.

All values

Identity and composition 5
Mechanical 5
Design values 5
Physical 1
Thermal 5
Optical 2
Electrical and magnetic 1
Fire not yet
Chemical and durability not yet

Mechanical

Elastic

Modulus of elasticity E

Young's modulus for design.

Condition	Value	Evidence
	70 000MPa	Corroborated1

Shear modulus G

G = E / 2(1 + ν).

Condition	Value	Evidence
	29 166MPa	Corroborated1

Poisson's ratio ν

In the elastic range.

Condition	Value	Evidence
	0.2	Corroborated1

Strength

Characteristic bending strength fg,k / fb,k

fg,k for annealed glass, fb,k for prestressed glass (5 % fractile).

Condition	Value	Evidence
	120MPacharacteristic	Confirmed

Knoop hardness HK

Resistance to indentation (ISO 9385 for glass).

Condition	Value	Evidence
	6GPa	Corroborated

Design values

Modification factor for load duration kmod

Multiplies characteristic strength: fd = kmod · fk / γM. Timber and glass are weaker under long-lasting loads (timber also when wet).

Condition	Value	Evidence
	1	Single source
	0.49	Single source
	0.32	Single source

Partial factor for the material γM

Recommended value; each country may set its own in the National Annex (a Nationally Determined Parameter).

Condition	Value	Evidence
	1.8	Single source
	1.2	Single source

Physical

Density ρ

Mass per unit volume.

Condition	Value	Evidence
	2 500kg/m³	Confirmed

Thermal

Coefficient of thermal expansion α

Linear, near room temperature.

Condition	Value	Evidence
	9×10⁻⁶ /K	Corroborated1

Specific heat capacity cp

Heat needed to warm 1 kg by 1 K.

Condition	Value	Evidence
	720J/(kg·K)	Corroborated1

Softening temperature Tso

Where the material starts to deform under its own weight.

Condition	Value	Evidence
	725°C	Single source1

Resistance to temperature difference ΔT

Temperature difference across a pane (sun and shade, sudden change) it is taken to survive.

Condition	Value	Evidence
	40K	Single source

Thermal conductivity λ

Heat flow through 1 m of material per kelvin of temperature difference.

Condition	Value	Evidence
	1W/(m·K)	Single source1

Optical

Refractive index n

Speed of light in vacuum over speed in the material.

Condition	Value	Evidence
	1.5	Single source1

Emissivity ε

Thermal radiation emitted relative to a black body; low-e coatings reduce it.

Condition	Value	Evidence
	0.837	Single source

Electrical and magnetic

Electrical resistivity ρe

Resistance of a 1 m cube between opposite faces.

Condition	Value	Evidence
	5 × 10⁷Ω·m	Single source

Chemical composition

Show on the periodic table

EN 572-1, proportion by mass of element (soda-lime silicate glass)

Element	Applies to	Range %	Evidence
Si	all thicknesses	32–35	Single source
Na	all thicknesses	7.4–11.9	Single source
Ca	all thicknesses	3.5–10.1	Single source
Mg	all thicknesses	0–3.7	Single source
Al	all thicknesses	0–1.6	Single source

Others below 5 %. As oxides (Vas Glass): SiO₂ 69–74 %, Na₂O 10–16 %, CaO 5–14 %, MgO 0–6 %, Al₂O₃ 0–3 %.

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With any other grade

Sources here are public pages that reproduce EN 12150-1. For design and acceptance, the standard edition named in your specification and the CE marking and Declaration of Performance of the delivered product take precedence. Design factors are recommended values; your National Annex may set others.