Low-E Glass Explained: Is It Worth the Extra Cost?

Low-E (low emissivity) glass has a microscopically thin metallic coating that reflects infrared heat while allowing visible light to pass through. It's one of the most effective thermal upgrades available for windows and doors, and it has become standard in most quality double glazed units. Here's what it does, how it works, and whether it's worth the extra cost for your project.

The Problem Low-E Solves

Standard clear glass is surprisingly poor at controlling heat. It lets visible light through well — that's the point — but it also freely transmits infrared radiation (heat). In winter, radiant heat from inside the building passes through the glass and is lost to the cold outside. In summer, solar infrared radiation pours in and heats the interior. Low-E coating addresses both problems with a single product.

How the Coating Works

A standard clear glass pane has an emissivity of approximately 0.84 — meaning it absorbs and re-emits 84% of the infrared radiation it receives. A low-E coating reduces this to 0.10–0.20. The coating acts as a one-way thermal mirror: it reflects heat back toward its source. In winter, heat generated inside reflects back into the room. In summer, solar heat is reflected away before it enters. The result is a building that's easier to heat in winter, cooler in summer, and cheaper to run year-round.

Types of Low-E Coatings

There are two main types of low-E coating with different properties and applications.

Hard coat (pyrolytic) is applied during the glass manufacturing process while the glass is still hot in the furnace. The coating bonds directly to the glass surface and is very durable — it can be used in single-glazed applications or left exposed on the surface of a double-glazed unit. Hard coat is slightly less thermally efficient than soft coat but more forgiving in terms of handling and installation.

Soft coat (sputtered) is applied in a vacuum chamber after manufacturing, using a process called magnetron sputtering. This produces a higher-performing coating with lower emissivity — down to around 0.02–0.04 in the best products. However, soft coat is fragile and oxidises rapidly if exposed to air. It must be sealed inside a double-glazed unit with the coated surface facing into the air gap. Soft coat is the type used in most high-performance IGUs.

Solar Control vs. Thermal Retention

Modern low-E coatings are engineered for specific climates and orientations. Understanding the difference between coating types is important for correct specification.

High solar gain coatings are designed for cold climates where passive solar heating is desirable. They allow more solar energy through the glass while still reflecting indoor radiant heat back inside. This is appropriate for south-facing windows in cool Australian climates or north-facing windows where you want to capture winter sun.

Low solar gain coatings suit hot climates or problematic orientations — west-facing windows in Brisbane, large north-facing glazing in Darwin. They block more solar heat to reduce cooling loads, at the cost of reduced passive solar benefit in winter.

When specifying low-E glass, always check both the U-value (thermal resistance) and the Solar Heat Gain Coefficient (SHGC). Your glass supplier can recommend the right product for the orientation and climate zone. Don't just ask for "low-E" without specifying which type.

Performance Numbers

To understand the real-world impact, here are approximate U-values for common configurations: • 6mm single clear: 5.8 W/m²K • 6/12/6 double with air: 2.7 W/m²K • 6/12/6 double with air and low-E: 1.8 W/m²K • 6/16/6 double with argon and low-E: 1.2–1.4 W/m²K • Triple glazing with low-E and argon: 0.6–0.9 W/m²K

The combination of low-E coating and argon gas fill (denser than air, lower thermal conductivity) gives the best thermal performance available in a standard double-glazed unit without moving to triple glazing.

Condensation Reduction

One practical benefit of low-E glass that customers notice immediately is reduced condensation on the inner pane. Condensation forms when the glass surface temperature drops below the dew point of the room air. With standard double glazing on a cold night, the inner pane can get quite cold — enough to form significant condensation. Low-E coating keeps the inner pane substantially warmer, dramatically reducing or eliminating condensation. For customers who currently struggle with moisture, drips, or mould around window frames in winter, this alone often justifies the upgrade.

Cost vs Benefit

Low-E glass adds roughly 15–25% to the cost of the glass component. In the context of a complete IGU including spacer, sealant, gas fill, and installed labour, the percentage increase on the total job cost is typically 8–15%. For most residential and commercial applications, the energy savings pay back this premium within 3–7 years. For large glazed areas, west-facing windows, or climates with significant heating or cooling costs, the payback is faster.

The Glazing Calculator can calculate the total area and weight of your panels — useful for working out how much low-E glass you need and getting accurate pricing from your supplier.

When to Recommend Low-E

Low-E makes the most sense for: • Any double-glazed unit in a new build or major renovation — the incremental cost is small relative to the total job • West and north-facing windows in warm Australian climates (solar gain control) • South-facing windows and large glazed areas in cold climates (thermal retention) • Properties targeting energy efficiency ratings or green building certification • Customers who want to reduce energy bills and improve year-round comfort

Frequently Asked Questions

Can low-E glass be used in single-glazed applications?

Hard coat low-E can be used as single glazing. Soft coat cannot — it must be sealed inside an IGU. For single-glazed retrofits where thermal performance is the goal, secondary glazing or full IGU replacement is usually more cost-effective than hard coat single glazing alone.

Does low-E glass look different?

Modern low-E coatings are nearly invisible to the eye in normal use. Some products have a very slight colour shift visible when viewed at an angle — often a subtle blue or green tint. Visible light transmission is minimally affected. Most customers cannot tell the difference between low-E and standard glass by looking through it.

Will low-E stop my room from getting warm from winter sun?

This depends on the coating type. High solar gain low-E coatings allow solar energy through while reflecting indoor radiant heat. If passive solar heating matters for your project, specify a high SHGC coating for north-facing windows and discuss orientation with your supplier.

How long does the coating last?

Soft coat low-E sealed within an IGU will last as long as the unit's edge seal — typically 20–25 years. If the seal fails and the unit fogs, the coating may also degrade. Hard coat on an exposed surface is more durable and can last decades. Quality installation and appropriate frame design extend both.

How can you tell if glass has a low-E coating?

Hold a lit match or pen light near the glass. Standard glass reflects two images (front and back surface). Low-E glass reflects a third image with a different colour — typically orange or green — from the metallic coating. Glazing professionals also use dedicated low-E detection tools that give a definitive result in seconds.