Eight types of window glass compared across strength, safety classification, UV protection, thermal performance, and break pattern. From standard float glass to high-performance insulated glass units, each type serves a distinct purpose in residential and commercial construction.
Last Updated: March 2026
Comprehensive comparison of all major window glass types by performance characteristics. Strength is relative to standard annealed float glass.
| Glass Type | Strength | Safety Rating | UV Block | Thermal Perf. |
|---|---|---|---|---|
| Float (Annealed) | 1x (baseline) | Non-safety | 25-30% | Poor (U-factor 1.04) |
| Tempered | 4-5x annealed | Safety glazing | 25-30% | Poor (U-factor 1.04) |
| Heat-Strengthened | 2x annealed | Non-safety | 25-30% | Poor (U-factor 1.04) |
| Laminated | 1-2x annealed | Safety glazing | 95-99% | Poor-Fair (U-factor 0.95) |
| Low-E Coated | 1x (with coating) | Non-safety (unless tempered) | 75-95% | Good (U-factor 0.35-0.45) |
| Tinted | 1x annealed | Non-safety (unless tempered) | 40-70% | Fair (SHGC 0.35-0.55) |
| Wired | 0.5x annealed | Fire-rated (not impact) | 25-30% | Poor (U-factor 1.04) |
| Insulated (IGU) | Varies by panes | Varies by panes | 75-99% (with Low-E) | Excellent (U-factor 0.25-0.35) |
Float glass is the base material for all other glass types. Manufactured by floating molten glass on a bed of molten tin at approximately 1,100 degrees C, producing a perfectly flat, uniform sheet with parallel surfaces. Standard float glass is 83-86% transparent to visible light and has a slight green tint from iron oxide content. Available in thicknesses from 2mm to 25mm. Float glass breaks into large, sharp, potentially dangerous shards, which is why it requires secondary processing (tempering or laminating) for safety-critical applications.
Created by heating float glass to approximately 620 degrees C and rapidly cooling both surfaces with jets of air (quenching). This creates a compressive stress layer on the surfaces and tensile stress in the core, making the glass 4-5 times stronger than annealed glass. Tempered glass must be cut and shaped before tempering -- it cannot be cut, drilled, or edge-worked after treatment without shattering. When it breaks, the entire pane disintegrates into small granular pieces approximately 6mm in size.
Two or more glass plies bonded together with a plastic interlayer, most commonly PVB (polyvinyl butyral) at 0.38mm or 0.76mm thickness. The interlayer provides three key benefits: safety (glass adheres to the interlayer when broken), UV protection (PVB blocks 95-99% of UV radiation), and sound dampening (PVB absorbs acoustic vibration). SGP (SentryGlas Plus) interlayer is 5x stiffer and 100x more tear-resistant than PVB, used for structural and security applications.
Low-emissivity coating consists of microscopically thin layers of metallic oxide (typically silver) deposited on the glass surface. Soft-coat Low-E (sputtered in a vacuum) reflects 92-95% of infrared radiation and is the standard for modern energy-efficient windows. Hard-coat Low-E (pyrolytic, applied during float manufacturing) reflects 85-88%. Low-E coatings reduce the U-factor of an IGU by 30-50% while maintaining 70-80% visible light transmission. Position on surface 2 or 3 depends on climate optimization priorities.
Tinted glass is produced by adding metallic oxides to the glass batch during manufacturing. Iron oxide creates green tint, cobalt oxide creates blue, selenium produces bronze, and nickel oxide creates gray. Tinting reduces solar heat gain (SHGC) and glare while adding aesthetic color. Bronze and gray are the most common architectural tints. Tinted glass absorbs solar energy and heats up, which can cause thermal stress breakage if not properly heat-strengthened. Heavily tinted glass may require heat strengthening for large pane sizes.
An IGU consists of two or three glass panes separated by sealed spacer bars and filled with insulating gas (typically argon or krypton). The sealed cavity reduces heat transfer by convection, while Low-E coatings on interior surfaces reduce radiative heat transfer. A standard double-pane IGU with Low-E and argon achieves U-factor 0.25-0.30 compared to U-factor 1.04 for a single pane -- a 70-75% improvement in insulation. IGU seals typically last 15-25 years before the gas fill begins to leak.
Building codes (IRC Section R308) require tempered or laminated safety glazing in specific locations where the risk of human impact is elevated.
All glass must be safety glazed regardless of size or height
All glass within the door panel must be safety glazed
Glass within 24 inches of either edge of a door
Any glazing with bottom edge less than 18 inches above the floor
Glass within 36 inches horizontally of a walking surface of stairways or landings
Glass within 60 inches of the water edge, less than 72 inches above walkway
Most modern residential windows use insulated glass units (IGUs) consisting of two panes of float glass with a sealed air or gas-filled cavity between them. The exterior pane typically has a Low-E coating to reflect infrared heat, and the cavity is filled with argon gas for improved insulation. The individual panes are usually 3mm or 4mm thick annealed (float) glass. In locations where safety glazing is required by code -- such as near doors, in bathrooms, or at low heights -- tempered or laminated glass is used instead of standard annealed glass.
Tempered glass is heat-treated to be 4-5x stronger than annealed glass and breaks into small, relatively harmless granular pieces. Laminated glass bonds two or more glass panes with a PVB or SGP interlayer -- when broken, the glass fragments adhere to the interlayer instead of falling. Tempered glass is stronger against impact but provides no post-breakage integrity. Laminated glass is slightly less impact-resistant but holds together when broken, providing continued barrier protection. Tempered glass is standard for shower doors and side windows. Laminated glass is standard for windshields, skylights, and security glazing.
Low-E (low-emissivity) glass has a microscopically thin metallic coating that reflects 85-95% of infrared radiation while allowing most visible light to pass through. This keeps heat inside during winter and blocks solar heat during summer. Low-E glass reduces window U-factor by 30-50% compared to uncoated glass and is essential for meeting ENERGY STAR requirements. In the DMV climate with both heating and cooling seasons, Low-E glass typically saves $100-300 per year in energy costs for a typical home. It is absolutely worth the modest premium of 10-15% over uncoated glass.
Traditional wired glass (with an embedded wire mesh) is being phased out. It was originally used as fire-rated glazing because the wire holds the glass in place when cracked by heat. However, wired glass is actually weaker than standard annealed glass -- the wire creates stress points and reduces impact resistance by approximately 50%. Modern fire-rated glass alternatives such as ceramic glass (Pyran, FireLite) and intumescent laminated glass provide fire ratings of 20-90 minutes while being 2-6x stronger than wired glass. Many jurisdictions no longer allow wired glass in hazardous locations.
For single-pane strength, heat-strengthened laminated glass with SGP (SentryGlas Plus) interlayer is the strongest commercially available option. It withstands approximately 2x the impact of standard tempered glass while maintaining post-breakage integrity. Tempered glass alone is 4-5x stronger than annealed glass but shatters completely on failure. For multi-layer security applications, laminated glass with multiple plies (such as 3-ply or 5-ply laminates) can resist forced entry, ballistic impact, and blast forces depending on the total glass and interlayer thickness.
Tinted glass reduces solar heat gain by absorbing a portion of solar radiation before it enters the building. Bronze tint blocks approximately 25-45% of solar energy. Gray tint blocks 30-50%. Green tint blocks 25-40% while transmitting slightly more visible light than bronze. However, tinted glass absorbs heat and re-radiates some of it inward, making it less effective than Low-E coatings for energy reduction. The best energy performance combines Low-E coating with a light tint on the exterior pane. Heavily tinted glass also reduces visible light transmission, requiring more artificial lighting.
For the best sound reduction, use an asymmetric insulated glass unit with a laminated outer pane and acoustic PVB interlayer. A configuration of 6.8mm acoustic laminated + 16mm air gap + 6mm glass achieves STC 42-45, reducing perceived noise by approximately 75%. Standard double-pane windows achieve STC 28-32. For even higher performance, triple-pane configurations with laminated outer panes can reach STC 45-50. The PVB interlayer in laminated glass dampens sound vibration, while the air gap provides physical separation -- both mechanisms work together.
Our glass experts help homeowners and businesses across the DMV area select the optimal glass type for every application. Free consultations and estimates, backed by our Comprehensive Warranty.
Take advantage of our special offers and save on your glass project.