What Is an Insulated Glass Unit (IGU)? Singapore Guide

Home › Blog › What Is an IGU? Glass Technology What Is an Insulated Glass Unit (IGU)? A Complete Guide for Singapore Homeowners By EZZO.SG Editorial · 15 July 2025 · 7 min read · Glass Technology If you have ever pressed your palm against a single-pane window on a sunny Singapore afternoon, you already understand the problem. The glass is almost too hot to touch, your air-conditioner runs non-stop, and every passing bus or MRT train finds its way straight into your living room. For the vast majority of homes built before the mid-2010s, a single sheet of glass — 6 mm at most — stands between you and the full force of the equatorial sun. An insulated glass unit , or IGU, changes that equation entirely, and understanding how it works is the first step to making a genuinely informed decision about your doors, windows or skylights. What Exactly Is an Insulated Glass Unit? An insulated glass unit is a pre-manufactured assembly of two or more panes of glass separated by a hermetically sealed gap. The gap — typically filled with argon or another inert gas — acts as a thermal and acoustic barrier between the exterior environment and your interior space. Unlike a single pane, which conducts heat directly from one face to the other, an IGU interrupts that conduction path at multiple points. The term "double glazing" is often used interchangeably with IGU in everyday speech, and in most residential applications the two terms describe the same thing: a two-pane assembly. Triple glazing — three panes with two sealed cavities — exists but is comparatively rare in Singapore, where acoustic performance and solar heat gain are the primary concerns rather than sub-zero winter cold. Key concept: An IGU is not simply two panes of glass placed next to each other. The sealed cavity, the spacer bar chemistry, and the choice of gas fill all work together as an engineered system. Replacing just one element — say, the glass — without considering the others leaves significant performance on the table. The Anatomy of an IGU — Layer by Layer A standard double-glazed IGU consists of four principal components. Each plays a distinct role, and the overall performance of the unit is only as good as its weakest element. OUTER PANE ARGON GAS CAVITY INNER PANE ARGON GAS Thermal conductivity ≈ 0.016 W/m·K LOW-E ② 5 mm 20 A or 27 A 5 mm SPACER SPACER Cross-section of a 5mm + 20A + 5mm IGU — the standard EZZO.SG configuration. The LOW-E coating sits on Surface ② (inner face of the outer pane), protected inside the sealed cavity. Outer Pane The outer pane is the first line of defence against the exterior environment. In Singapore — where afternoon sun angles are steep and UV intensity is high year-round — this pane is almost always tempered safety glass . Tempering involves heating the glass to approximately 620 °C and then rapidly cooling it, creating a pre-stressed surface layer. Should tempered glass break, it shatters into small, blunt fragments rather than dangerous shards — meeting the safety requirements for high-rise glazing under Singapore Building and Construction Authority (BCA) guidelines. The outer pane is also the ideal location for a LOW-E coating, positioned on its inward-facing surface (Surface ② in glazing notation). Here it is shielded from direct environmental contact while still intercepting incoming solar radiation before it enters the cavity. Spacer Bar Running along the perimeter of the unit, the spacer bar performs two jobs simultaneously: it holds the two panes apart at a precise, consistent distance, and it contains the desiccant material that absorbs any residual moisture inside the sealed cavity. Conventional spacer bars are hollow aluminium — effective at holding geometry, but also an excellent thermal conductor. A traditional aluminium spacer creates a thermal bridge at the edge of every unit, allowing warmth to flow between panes precisely where the sealed cavity ends. Modern warm-edge spacers , made from materials such as stainless steel, foam or composite polymer, significantly reduce this edge conduction and are increasingly standard on premium IGUs. Gas Fill The cavity is filled with an inert gas — typically argon — rather than air. Argon is denser than air and has a lower thermal conductivity (approximately 0.016 W/m·K versus air's 0.024 W/m·K), which means convective heat transfer across the cavity is meaningfully reduced. The gas is sealed into the unit at the factory under controlled conditions, ensuring consistent fill levels and no contamination. Inner Pane The inner pane — facing your interior — is typically the same tempered specification as the outer pane for safety compliance, though the glass type may vary. A clear inner pane allows maximum visible light transmission; a tinted inner pane can further reduce solar gain without heavy reflective coatings on the exterior. Why the Spacer Bar and Gas Fill Matter These two components are the ones most commonly glossed over in product brochures, yet they are largely responsible for the real-world performance difference between an average IGU and an excellent one. Heat moves through a window via three mechanisms: conduction (through the glass and frame), convection (currents within the gas cavity), and radiation (electromagnetic energy re-emitted from warm surfaces). A LOW-E coating addresses radiation. The gas fill addresses convection. The spacer bar addresses edge conduction. An IGU that optimises all three mechanisms will consistently outperform one that neglects any of them. Why argon over air? Argon gas has roughly 34% lower thermal conductivity than air. In practice, an argon-filled IGU can reduce the U-value (heat flow rate) of the assembly by 10–15% compared to an identical air-filled unit. Over Singapore's year-round cooling season, that difference translates directly into measurable energy savings — and a quieter, more stable interior temperature. The cavity width also matters. A gap under 10 mm does not provide enough space to suppress convective currents effectively. A gap beyond around 20–24 mm for argon allows large convective cells to form, which actually increases heat transfer rather than reducing it. The sweet spot for argon-filled IGUs sits between 12 mm and 20 mm — which is precisely the range EZZO.SG's standard 20 mm cavity (the "20A" in 5mm+20A+5mm notation) is designed to exploit. The wider 27 mm option pushes slightly beyond this sweet spot in the interest of acoustic mass, a deliberate trade-off that makes sense for high-noise environments. IGU Glass Specifications: What the Numbers Mean When you see a glazing specification written as 5mm+20A+5mm or 5mm+27A+5mm , you are reading a shorthand description of the unit's cross-section from exterior to interior. Each segment is explicit: 5mm — Thickness of the outer glass pane. In all EZZO.SG products, this is tempered safety glass. 20A or 27A — Width of the sealed cavity in millimetres, where "A" denotes argon gas fill. 5mm — Thickness of the inner glass pane, also tempered in EZZO.SG configurations. The overall unit thickness is therefore 30 mm for the standard configuration (5 + 20 + 5), or 37 mm for the wider-cavity option (5 + 27 + 5). Comparison of EZZO.SG 5mm+20A+5mm and 5mm+27A+5mm insulated glass units Property 5mm + 20A + 5mm 5mm + 27A + 5mm Total unit thickness 30 mm 37 mm Cavity width 20 mm 27 mm Gas fill Argon (standard) Argon (standard) Typical U-value with LOW-E ~1.5–1.8 W/m²K ~1.3–1.6 W/m²K Acoustic performance (Rw, est.) 30–33 dB 33–36 dB Glass type options Clear / LOW-E / Tinted / Smart / Coated Clear / LOW-E / Tinted / Smart / Coated Best suited for Standard residential, offices, north-facing High-traffic roads, MRT proximity, west-facing LOW-E coating explained. LOW-E (Low Emissivity) glass has a microscopically thin metallic oxide coating — often silver-based — applied to one surface of the unit. This coating reflects long-wave infrared radiation (heat) back toward its source. In Singapore's climate, the coating