All posts by Eduardo Savin

Where Low-E Coatings Are Placed Inside an IGU (and Why It Matters) 

For low-E glass to perform correctly, it’s not enough to select the right type of coating. Its placement inside the insulated glass unit (IGU) is equally important. 

A standard double-pane IGU has four possible surfaces: 

• Surface #1: the exterior face exposed to the outdoor climate 

• Surface #2: the internal face of the first lite, facing the airspace 

• Surface #3: the internal face of the second lite, also facing the airspace 

• Surface #4: the interior face of the glass, inside the building 

Thermal and solar performance can change significantly depending on which surface receives the low-E coating. 

Solar Control Low-E → Best on Surface #2 

• Soft coat solar control low-E coatings perform best on surface #2, because they: 

• Block most of the infrared radiation entering from the exterior 

• Reduce solar heat gain in warm or mixed climates 

• Maintain high visible light transmission while lowering heat load 

For this reason, low-E coatings are applied to this surface for most modern residential and commercial windows. 

Passive Low-E (Hard-Coat) → Best on Surface #3 or #4 

Passive low-E coatings are designed to retain heat and often allow some short-wave solar energy to enter. They are typically applied to: 

• Surface #3: ideal for conserving interior heat while still benefiting from solar gain 

• Surface #4: excellent for cold climates, reflecting interior radiant heat back inside 

This configuration allows windows to function as passive solar collectors during winter months. 

Choosing the right surface ensures: 

• Better energy efficiency 

• Improved solar control 

• Reduced thermal transfer 

• Longer IGU lifespan 

• Optimized UV protection 

Many window performance issues, such as condensation, overheating, or poor insulation, occur when low-E coatings are applied to the wrong surface. 

Benefits of Low-E Glass in Modern Windows and Facades 

Far beyond the technical aspects, low-E glass has become a defining trend in modern U.S. architecture. This is due to the real, measurable benefits it brings to window and facade systems. These are the most important ones:

1. Greater energy efficiency and reduced consumption

Low-E glass minimizes heat transfer into the interior during summer and prevents heat from escaping during winter. 

This results in: 

• Lower air-conditioning usage 

• Reduced heating demand 

• Lower annual energy costs 

Even small improvements in U-factor and SHGC values can generate significant savings in extreme climates.

2. Year-round thermal comfort

Windows maintain a more stable interior temperature. With low-E glass you avoid: 

• Excessive heat near sun-exposed windows 

• “Cold wall effect” during winter 

The result is a more comfortable and consistent indoor environment.

3. UV protection and reduced interior fading

Low-E glass blocks a significant portion of ultraviolet radiation, the main cause of: 

• Fading of wood floors 

• Deterioration of textiles and carpets 

• Damage to furniture and interior finishes 

This is one of the most valued advantages in premium residential projects.

4. Better visual comfort without sacrificing natural light

Unlike tinted or reflective glass, low-E maintains high visible light transmission: 

• Reduces glare 

• Maintains more balanced color rendering 

• Preserves visual clarity 

It’s ideal for large windows, curtain walls, or any architecture that relies on natural daylight.

5. Improved overall performance when used in IGUs

When paired with insulated glass units (IGU), low-E coatings enhance: 

• Thermal insulation 

• Acoustic insulation 

• Solar control 

• Durability of seals and components 

This is why low-E glass has become the standard choice for modern high-performance window systems. 

Low-E Windows by Climate: How to Choose the Right Type 

The ideal type of low-E glass depends directly on the climate where it will be installed. Although all low-E coatings improve energy efficiency, each performs better under specific environmental conditions. 

Cold climates (long winters) 

• Goal: retain interior heat and maximize passive solar gain 

• Recommended: hard coat low-E (pyrolytic) 

Why it works: 

✅ Allows more solar heat gain (higher SHGC) 

✅ Reduces interior heat loss 

✅ Ideal for homes with constant heating needs 

Warm climates or regions with high solar exposure 

• Goal: block solar heat gain and reduce air-conditioning consumption 

• Recommended: soft coat low-E (solar control) 

Why it works: 

✅ Low SHGC to minimize incoming heat 

✅ Better UV protection 

✅ Cooler and more stable interior environments 

Mixed climates (most of the U.S.) 

• Goal: balance performance between hot and cold seasons 

• Recommended: high-performance soft coat low-E 

Why it works: 

✅ Optimal insulation during winter 

✅ Advanced solar control in summer 

✅ Excellent efficiency-to-cost ratio 

Coastal regions or areas prone to storms 

In addition to low-E glass, the system should be reinforced with: 

• IGU with argon gas 

• Laminated glass for increased impact resistance 

• High-performance seals 

Ideal configuration: 

✅ Soft coat low-E + IGU + laminated glass 

✅ Projects requiring maximum visual clarity 

✅ For large window walls or façade systems where aesthetics are a priority: 

✅ Soft coat low-E with high visible light transmission (VLT) 

✅ Neutral coatings without noticeable blue-green tint 

Low-E Glass vs. Clear Glass: When Is It Worth the Investment? 

Although clear glass is still a common choice for standard residential windows, its thermal and solar performance is extremely limited. The difference between a system with low-E glass and one with clear glass is so significant that, in most modern projects, low-E is no longer a luxury, it’s a technical requirement. 

Below is a direct comparison that explains when and why low-E glass is worth the investment. 

Low-E glass is no longer considered a “premium” option. It’s become a technical requirement for today’s windows, doors, and façade systems. 

Its ability to reduce energy consumption, improve thermal comfort, block UV radiation, and maintain optimal levels of natural light makes low-E one of the most efficient materials for residential and commercial applications.  

Whether in warm, cold, or mixed climates, low-E glass acts as an intelligent thermal regulator, delivering measurable benefits to both building design and long-term performance. 

For architects, developers, and contractors, specifying low-E glass means: 

• Better energy performance 

• More stable indoor comfort throughout the year 

• Extended protection for interiors and finishes 

• More durable and efficient IGU systems 

• A real value-add for any project 

This is why low-E glass has become the industry standard. It’s also why PRL Glass offers one of the most complete low-E product lines that’s adaptable to every climate, system type, and performance requirement. 

👉 Request low-E samples and technical sheets for your next project. Our team can help you select the right low-E configuration. Whether it’s a hard coat, soft coat, or IGU with a laminated interlayer or argon-filled gas, we can help you maximize energy performance and comfort in your designs.