How Clear Glass Is Turned Into Low-E Glass
All Low-E glass starts as clear glass. Clear glass allows unfiltered sunlight to pass through, bringing in natural light while also allowing heat and UV rays to enter. This can increase your energy bills and cause furniture, flooring, and window treatments to fade.
To improve performance, clear glass is treated with a low-emissivity (Low-E) microscopic coating. This low-emissivity film is an ultra-thin layer of metal, typically made of silver or a similar reflective material, applied to the surface of the glass. It’s designed to reflect heat back to its source, keeping warm air inside during winter and outside during summer. The coating is so thin that it’s virtually invisible to the naked eye (approximately 500 times thinner than a piece of human hair), yet it dramatically changes how the glass behaves. There are two main ways Low-E coatings are applied:
- Hard coat (pyrolytic) is applied while the glass is still hot during manufacturing, fusing the transparent coating into the surface. This version is more durable and can be used in single-pane applications.
- Soft coat (sputter-coated) is applied in a vacuum chamber after the glass has cooled. It offers higher performance in terms of insulation and UV protection, but it’s typically used in insulated triple- and double-pane glass units.
The result is a high-performance glass that resembles standard clear glass but works significantly better, reducing heat transfer, filtering UV light, and helping your home stay comfortable throughout the year.
Is Low-E Glass Worth the Cost?
Installing windows and doors with Low-E glass has a higher initial cost, but its energy-saving benefits, improved comfort, and UV protection deliver significantly more value over time. The table below offers a side-by-side comparison between Low-E and untreated glass.
| Factor | Low-E Glass | Clear Glass |
| Initial Cost |
10–15% higher than standard glass |
Lower upfront cost |
| Energy Efficiency | Reduces energy loss by 30–50% | Minimal insulation; higher energy loss |
| Annual Energy Savings | $71–$501 annually, depending on climate and window and door area | Negligible savings |
| UV Protection | Blocks up to 99% of UV rays | Allows most UV rays; risk of fading |
| Comfort | Maintains stable interior temperatures; minimizes hot spots and drafts | Prone to heat loss and temperature swings |
| Long-Term Value | Pays for itself in savings; can boost resale value | Lower cost now; less efficient long-term |
How Do Low-E Windows Affect Window Performance Ratings?
When evaluating replacement windows and doors, three key performance metrics to consider are U-Factor, Solar Heat Gain Coefficient (SHGC), and Visible Transmittance (VT). These ratings, provided by the National Fenestration Rating Council (NFRC), indicate how well your window or door will perform in terms of insulation, solar control, and natural light.
| Metric | What It Measures | Why It Matters | Clear Double-Pane | Low-E Double-Pane | Low-E Impact |
| U-Factor | The rate of heat loss through the window | Lower values = better insulation. Critical for cold-weather performance. | ~0.48 | ~0.30 – 0.35 | Reflects interior heat back into the home, reducing heat loss |
| SHGC | How much solar heat passes through the glass | Lower values help reduce overheating in warmer months or sunny exposures | ~0.55 | ~0.25 – 0.40 | Reflects infrared solar energy, reducing heat gain while keeping spaces bright |
| VT | The percentage of visible light that enters through the glass | Higher values = more natural daylight indoors | ~0.70 – 0.75 | ~0.55 – 0.65 | Slight reduction in light transmission with modern coatings that minimize impact. |
How Do Low-E Glass Windows Perform in Different Climates Compared to Clear Glass?
The choice between Low-E glass and clear glass often comes down to how they perform in your region’s climate. While they may look nearly identical, their impact on home comfort and ability to improve energy efficiency can vary widely depending on temperature, sun exposure, and seasonal extremes.
Cold Climates
In regions with long, cold winters, such as the Pacific Northwest, the Midwest, or the Northeast, Low-E glass significantly reduces heat loss. Its metallic coating reflects interior heat back into the home, keeping living spaces warmer without overworking your heating system. Clear glass, by contrast, allows that heat to escape, resulting in cold drafts and higher utility bills.
Hot, Sunny Climates
In places like Arizona, Texas, or Southern California, the goal is blocking solar heat gain and reducing energy costs. Soft-coat Low-E glass excels in these areas by reflecting infrared light from the sun before it enters the home. This helps interiors stay cooler, reduces glare, and limits UV damage to flooring and furnishings. Clear glass provides no such protection, often making interior spaces feel hotter and more exposed.
Mixed or Mild Climates
In areas with mild, variable seasons, Low-E glass offers the best of both worlds. It limits heat loss in the winter while still shielding the home from UV rays and unwanted solar gain in the summer. Its performance is year-round, even on cloudy days when UV rays still penetrate untreated glass. Clear glass may initially appear neutral, but over time, it contributes to energy waste and interior fading.
When Should You Choose Low-E vs. Clear Glass?
Each home and project has its priorities. Some focus on energy savings, while others are driven by budget or design considerations. The table below simplifies your decision by matching common goals with the best type of glass for the job.
| Situation or Goal | Best Glass Type |
| Lower monthly heating and cooling bills | Low-E Glass |
| Reduce indoor temperature swings and drafts | Low-E Glass |
| Maximize home energy efficiency | Low-E Glass |
| Live in a climate with cold winters or hot summers | Low-E Glass |
| Protect furniture, floors, and artwork from UV fading | Low-E Glass |
| Increase overall indoor comfort | Low-E Glass |
| Improve insulation in triple- and double-pane windows and doors | Low-E Glass |
| Upgrade main living areas like bedrooms, living rooms, or offices | Low-E Glass |
| Replace windows in a detached garage, shop, or shed | Clear Glass |
| Work within a limited or fixed renovation budget | Clear Glass |
| Need basic functionality in low-traffic areas (e.g. basement windows) | Clear Glass |
| Prefer maximum visible light with no coating or tint | Clear Glass |
| Want to preserve views with completely clear glass | Clear Glass |
| Plan to sell your home and want energy-efficient features for resale | Low-E Glass |
Make the Best Choice for Your Home
The right glass can do more than just let in the light. It can improve your home’s comfort, protect your interiors, and lower energy costs. For most homeowners in the Seattle area and beyond, Low-E glass offers a meaningful upgrade that pays off in year-round energy performance. Its ability to reflect heat, block ultraviolet light rays, and improve insulation makes it a solid choice for comfort and efficiency.
That said, regular glass windows and doors still have their place, especially in detached buildings, low-traffic areas, or budget-driven renovations where insulation and solar control are not as critical.
If you’re planning a replacement project or trying to decide which glass is right for your project, it helps to think long-term. The best approach often begins with a professional consultation that considers your home’s layout, local climate, and how each space is utilized. A knowledgeable professional can help you weigh your options and select the energy-efficient glass that best suits your home.
