When evaluating tempered glass quality, most buyers focus on strength, fragmentation, or surface defects. However, flatness is just as critical, especially for curtain walls, shower enclosures, railings, mirrors, and insulated glass units. The two most important flatness indicators are Overall Bow and Roller Wave, both specified in EN 12150, the European standard for thermally toughened safety glass.
Overall Bow refers to the overall curvature of the entire glass panel after tempering. During the heating and rapid cooling process, internal stresses are introduced into the glass, which may cause the panel to bend slightly. According to EN 12150, the overall bow should not exceed 0.3% of the glass length or width, depending on the measurement direction. Excessive bow can create alignment issues during installation, reduce the visual quality of façades, and affect the sealing performance of insulated glass units.
Roller Wave, on the other hand, is a localized surface distortion caused by the ceramic rollers inside the tempering furnace. It appears as small wave-like undulations running perpendicular to the roller direction. Although often invisible under normal conditions, roller wave becomes much more noticeable when glass is viewed in reflection, especially on large façades, Low-E glass, or dark-coated glass. EN 12150 specifies that roller wave should generally be no greater than 0.3 mm over a 300 mm measuring length, ensuring the glass maintains acceptable optical quality.
For modern architectural projects, simply meeting the EN 12150 requirement is often not enough. Large-format curtain wall glass, frameless railings, and high-end residential glazing demand even tighter flatness control to minimize optical distortion and simplify installation.
At MIGO Glass, we continuously optimize our tempering process, furnace temperature control, and roller calibration to achieve significantly better flatness than the standard requirement. Our production is capable of maintaining Overall Bow below 0.2%, delivering improved visual quality, easier installation, and more consistent performance for demanding architectural applications.
Meeting the standard is the minimum. Delivering better flatness is what sets high-quality tempered glass apart.
For more inquiry:
Email: Tracy@migoglass.com
WhatsApp: +86 15610010953
