Impact window and door glass is made from 2 sheets of glass with an interlayer of PVB (polyvinyl butyral) or SGP (SentryGlas Plus). The interlayer is what makes the window impact -resistant, and is the reason why impact windows crack, instead of shatter.
Most window manufacturers will use annealed laminated glass when designing an impact window. The term annealing refers to the process of cooling the glass. Annealed glass is created by slowly cooling hot glass after it has been formed. The controlled cooling removes internal stresses, making it durable for many applications. Annealed glass is also called plate glass, standard glass, or float glass. When using Annealed glass in impact windows and doors, it will be the PVB or SGP interlayer that makes the glass stronger.
Heat strengthened glass is usually a higher priced option for most manufacturers of impact windows and doors. Heat strengthened glass is annealed glass that has been heat treated. In this process, the glass is heated to about 1200° and force cooled. The process is then repeated several times. This process makes the glass 2 times stronger than annealed glass. The main advantage of heat strengthened glass is the outstanding resistance to stress cracking, which can happen when windows go through multiple handling processes, including transportation during shipping.
Key Differences summed up:
Strength: 2 times stronger than annealed glass.
Safety & Breakage: While neither is technically classified as “safety glass, heat strengthened has a slight advantage.
Applications: Heat strengthened is ideal for high wind areas and large panes, while annealed is suited for standard, less demanding residential impact resistant applications.
Cost: Annealed impact glass can be approximately 10-40% less expensive when compared to heat strengthened impact glass when comparing pricing from the same manufacturers pricing of “regular” impact glass (annealed) and heat strengthened impact glass.
In the end, while both annealed laminated and heat strengthened laminated glass are both impact rated for High Velocity Wind Zones, heat strengthened is generally the preferred choice for superior performance, while annealed provides a standard solution. Seascape Windows and Doors uses ESW windows and doors as our primary source of impact product, and all ESW products are made with heat strengthened glass as their standard – not and upgrade.
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