Heat-Strengthened

Purpose. Heat-strengthened glass of increased strength for facades, structural glazing and as a component of laminated glass — where strength above annealed glass is needed together with reduced risk of spontaneous breakage.

Construction and properties. Bending strength — 70 MPa (float glass) / 55 MPa (patterned glass), roughly double that of annealed glass, but lower than tempered glass. Thermal-shock resistance — withstands a temperature differential of at least 100 °C (per GOST). On breakage it forms large fragments that remain in the frame (on its own it is NOT classed as safety glass). Substantially less prone to breakage from NiS inclusions than tempered glass.

Governing standards. GOST 33087-2014 "Heat-strengthened glass. Technical specifications" (complies with Russian national standard, mandatory for the Russian market).

Points to note. Heat-strengthened glass used as a single pane is not classed as safety glass — it is almost always used as a component of laminated glass or in combination with tempered glass, so that the assembly as a whole meets breakage-safety requirements. Do not confuse "higher strength" with "safety on breakage" — these are different properties.