Insulated Glass Units — Guardian SunGuard® Window 64 & 70

Insulated glass units (IGUs), also called double-pane or dual glazed glass, seal two lites of glass around a precise airspace to dramatically reduce heat transfer compared to single-pane glazing. The result is lower energy bills, a more comfortable interior environment, reduced condensation on interior surfaces, and better noise control — all while maintaining clear, unobstructed views.

Custom Glass Industries stocks dual-glazed IGUs with Guardian SunGuard® Window 64 HT and SunGuard® Window 70 HT low-e coatings, available on standard Clear or UltraClear® glass substrates in 3mm (1/8"), 5mm (3/16"), and 6mm (1/4") thickness. All units are fabricated with the low-e coating on Surface 2 (interior face of the outboard lite) and a 1/2" (12.7mm) airspace filled with air or argon gas. Triple-glazed configurations are available by special order.

SunGuard® Window 64 HT vs. SunGuard® Window 70 HT — What's the Difference?

Both are triple-silver, high-performance low-e coatings from Guardian Glass, and both must be heat-treated (tempered or heat-strengthened) after coating application.

SunGuard® Window 64 HT delivers strong solar control (SHGC 0.28) with good visible light transmittance in the low-to-mid 60s. It is well suited for commercial storefronts, office glazing, and any application where keeping solar heat out is the top priority without significantly darkening the space.

SunGuard® Window 70 HT allows more visible light through (high 60s to 70%) while still providing meaningful solar control (SHGC 0.34–0.36). It is the better choice when maximizing natural daylight and views is equally important as energy performance — retail facades, curtain walls, and residential picture windows.

Clear vs. UltraClear®

Standard clear glass has a slight green tint, visible in thick lites and on edge. Guardian UltraClear® is a low-iron glass that removes that tint entirely, delivering a more neutral, bright appearance. The performance difference between Clear and UltraClear is modest — one to two percentage points in VLT — but the visual difference at the edge or in large spans is significant. UltraClear is popular for storefronts, entrances, and high-end architectural glazing.

Air vs. Argon Fill

All units can be filled with air or with argon gas. Argon is denser than air and slows heat transfer across the airspace, improving the U-Value by approximately 0.04–0.05 Btu/hr·ft²·F compared to an air-filled unit of the same configuration. Argon fill is recommended wherever energy code compliance or maximum insulating performance is required, and it adds minimal cost.

Performance Data — SunGuard® Window 64 HT (Surface 2 Coating, 1/2" Airspace)

Center-of-glass values, NFRC 2010. No framing or spacer effects included.

Performance Data — SunGuard® Window 70 HT (Surface 2 Coating, 1/2" Airspace)

Center-of-glass values, NFRC 2010. No framing or spacer effects included.

Understanding the Numbers

VLT (Visible Light Transmittance) — The percentage of visible daylight that passes through the unit. Higher means a brighter interior.

SHGC (Solar Heat Gain Coefficient) — How much of the sun's total solar energy passes through the glass. Lower means less solar heat enters the building; good for hot or sunny climates.

U-Value (Btu/hr·ft²·F) — How much heat flows through the glass due to the temperature difference between inside and outside. Lower means better insulation. Winter Night and Summer Day values differ because of how convective airflow behaves at different temperatures.

LSG (Light-to-Solar Gain) — The ratio of VLT to SHGC. Higher LSG means the glass delivers more visible light relative to the solar heat it allows in — generally desirable. SunGuard 64 HT's higher LSG reflects its strength as a daylighting-while-controlling-heat coating.

All performance values are center-of-glass, calculated per NFRC 2010 standard using the Guardian Performance Calculator. Actual whole-unit performance will vary with frame, spacer system, and installation conditions. HT/T coatings require heat treatment; specified values are valid only after heat treatment is complete.

Triple Glazed Units

For projects requiring the lowest possible U-factors — passive house, cold-climate construction, high-performance curtain walls — triple-glazed units with SunGuard 64 HT or 70 HT coatings are available by special order. Triple glazing with argon fill in both airspaces typically achieves center-of-glass U-values in the 0.18–0.22 range, a 30–40% improvement over equivalent dual glazed units. Ask us about lead time and sizing.

Applications

• Commercial storefronts, curtain walls, and office facades
• Retail and restaurant glazing where daylight and views matter
• Residential window and patio door replacement
• Skylights and sloped glazing
• Projects requiring energy code compliance (Title 24, ASHRAE 90.1, IECC)
• LEED and net-zero building programs

In-Stock Configurations

CGI currently stocks the following glass substrates ready for IGU fabrication:

• SunGuard® Window 64 HT — Clear: 3mm, 5mm, 6mm
• SunGuard® Window 64 HT — UltraClear®: 3mm, 5mm, 6mm
• SunGuard® Window 70 HT — Clear: 3mm, 5mm, 6mm
• SunGuard® Window 70 HT — UltraClear®: 3mm, 5mm, 6mm

Air or argon fill available on all configurations. Units can be tempered, heat-strengthened, or fabricated annealed depending on project requirements.

Have a spec sheet or need help selecting the right make-up for your project? Request a quote and our team will confirm availability and lead time.