The Heat Strengthening process is similar to Toughened Glass but with lower levels of surface compression, resulting from a lower cooling quench. Heat Strengthened Glass has a mechanical strength of about twice that of annealed or untreated glass.
Heat Strengthened Glass is typically specified when additional strength is needed to resist wind pressure, thermal stress or both, and when the strength or safety break pattern of fully Toughened Glass is not required. When broken, the glass fragments are more similar in size and shape to annealed glass fragments and thus tend to stay in the opening longer than fully Toughened Glass particles. Although Heat Strengthened Glass is NOT a safety glazing by Building Code, this breakage pattern prevents the glass from falling and injuring someone.