All posts by Eduardo Savin

What Is Hard Coat Low-E Glass? 

Hard coat low-E, also known as pyrolytic low-E, is a type of low-emissivity coating that’s applied directly to the glass during the manufacturing process, while the glass is still hot on the float line. 

Because of this process, the coating chemically fuses with the glass surface, resulting in an extremely durable and resistant layer. 

Characteristics of Hard Coat Low-E 

• Coating applied at high temperature (pyrolytic process) 

• High mechanical and chemical durability 

• Can be used as monolithic glass or integrated into an IGU 

• Higher solar heat gain compared to soft coat low-E 

• Low emissivity, though higher than soft coat low-E 

In simple terms, hard coat low-E reduces heat loss while allowing more solar energy to enter the building. 

Thermal Performance of Hard Coat Low-E 

Hard coat low-E primarily works as an interior heat reflector: 

• In winter, it reflects interior heat back into the space 

• Reduces heat loss through the glass 

• Takes advantage of direct solar radiation 

For this reason, it’s often associated with projects where solar heat gain is desirable rather than blocked. 

Typical Applications of Hard Coat Low-E 

Hard coat low-E is a suitable option for: 

• Cold climates with long heating seasons 

• Residential buildings with high heating demand 

• Projects that prioritize simplicity and coating durability 

• Applications where the glass may be exposed before being assembled into an IGU 

It’s also useful in projects where extreme solar control is not a priority, but basic energy efficiency and coating resistance are required. 

Limitations of Hard Coat Low-E 

Although it’s a reliable system, hard coat low-E has limitations when compared to soft coat low-E: 

• Less effective solar heat control in warm climates 

• Higher SHGC values 

• Lower overall performance in mixed or high-solar radiation climates 

• Doesn’t achieve the same energy efficiency levels as modern soft coat low-E within an IGU 

For these reasons, its use today is more specific and climate-dependent, and it’s generally recommended only when the project conditions clearly justify it. 

What Is Soft Coat Low-E Glass? 

Soft coat low-E, also known as solar control low-E, is a low-emissivity coating applied to glass using an off-line process called Magnetron Sputter Vacuum Deposition (MSVD). 

Unlike hard coat low-E, this coating is applied to cooled glass inside a vacuum chamber, allowing for much greater precision in thermal and solar performance control. 

The result is a microscopic, highly efficient coating, engineered to maximize thermal insulation and solar control, especially when integrated into an insulated glass unit (IGU). 

Key Characteristics of Soft Coat Low-E 

• Cold-applied coating (MSVD process) 

• Very low emissivity (significantly lower than hard coat) 

• High control of infrared (IR) and ultraviolet (UV) radiation 

• Must be protected within an IGU or laminated glass 

• Excellent energy performance in mixed and warm climates 

• Available in neutral, selective, or high solar-control versions 

In simple terms: soft coat low-E not only reduces heat loss, but actively blocks unwanted heat gain, without sacrificing natural daylight. 

Thermal and Solar Performance of Soft Coat Low-E 

Soft coat low-E acts as a high-performance thermal barrier: 

• In summer, it reflects a large portion of solar heat before it enters the interior 

• In winter, it helps retain interior heat when combined with an IGU 

• Significantly reduces the solar heat gain coefficient (SHGC) 

• Substantially improves the overall U-factor of the glazing system 

This balance makes it the most versatile low-E option for many contemporary projects in the United States. 

Typical Applications of Soft Coat Low-E 

Soft Coat Low-E is ideal for: 

• Mixed climates (most of the U.S.) 

• Warm or high solar-radiation regions 

• Facades with large glass openings 

• High-performance windows and doors 

• Premium residential projects and commercial buildings 

• Systems aiming to meet modern energy standards 

For these reasons, soft coat low-E is the most widely used low-E coating in modern window systems today. 

Important Considerations for Soft Coat Low-E 

• Despite its superior performance, soft coat low-E requires specific conditions: 

• Must be sealed within an IGU or laminated glass 

• Not designed for prolonged direct exposure 

• Requires controlled fabrication and handling 

These requirements are not disadvantages, but rather part of its advanced design to achieve maximum energy performance and durability. 

Low-E in IGU’s (Insulated Glass Units): Why It Maximizes Performance 

The true potential of low-E glass is achieved when it is integrated into an insulated glass unit (IGU). While low-E coatings already improve the thermal performance of glass on their own, combining them with an air or gas-filled cavity transforms the system into a high-performance solution for modern windows, doors, and façades. 

An IGU generally consists of: 

• Two or more glass panes 

• A sealed cavity between them (air or argon gas) 

• A perimeter spacer 

• Seals that ensure airtightness 

When low-E is strategically positioned within this unit, thermal and energy performance are significantly enhanced. 

Low-E Coating Placement Inside an IGU 

In a standard double-pane IGU’s, there are four possible glass surfaces: 

• Surface #1: Exterior face of the outer glass 

• Surface #2: Interior face of the outer glass 

• Surface #3: Exterior face of the inner glass 

• Surface #4: Interior face of the inner glass 

In most applications: 

👉 Soft coat low-E is installed on surface #2 or #3, protected inside the sealed cavity. 

This placement allows the coating to: 

• Reflect solar heat before it enters the interior 

• Retain interior heat during winter 

• Remain protected from physical or environmental damage 

Correct placement is critical to optimizing U-factors, SHGC, and overall indoor comfort. 

How Low-E Works Inside an IGU 

When low-E is part of an IGU, it: 

• Reflects infrared radiation depending on the season 

• Reduces heat transfer through conduction and radiation 

• Works together with argon gas to minimize energy loss 

• Maintains high visible light transmittance 

The result is a system that doesn’t just block heat but actively manages the energy entering and leaving the building. 

Key Benefits of Low-E + IGU’s 

The low-E + IGU combination delivers: 

• Significantly lower U-factors (better insulation) 

• Controlled SHGC, ideal for warm or mixed climates 

• Greater comfort near windows and large glazing areas 

• Reduced load on HVAC systems 

• Less condensation in cold climates 

• Increased durability of the overall glazing system 

For this reason, an IGU without low-E is now considered incomplete in modern architectural projects. 

Low-E in IGU’s for Advanced Applications 

In higher-performance projects, low-E within IGU’s can be combined with: 

• Argon or krypton gas for enhanced insulation 

• Laminated glass for safety, acoustic control, or impact resistance 

• Selective low-E coatings for highly sun-exposed façades 

• Triple-pane configurations for extreme climates 

This flexibility allows glass performance to be tailored to the specific needs of each project, without compromising aesthetics or visual clarity. 

Low-E glass reaches its maximum performance when it’s part of a well-designed IGU. It’s not just about the coating itself, but about the entire system working together as an intelligent thermal barrier. 

That’s why, in contemporary architecture, specifying low-E + IGU’s is no longer a premium option. It’s a logical technical decision to achieve long-term efficiency, comfort, and durability. 

• You may also be interested in reading: Low-E Glass vs Clear Glass: Real Performance Differences and When to Choose Each One