Double Glazed Units with vacuum insulation — the next generation of high-performance glazing technology, ASTM standards, and Low-E integration.
A Vacuum Insulating Glass (VIG) or Vacuum DGU is a double-glazed unit in which the space between two glass panes is evacuated to a near-vacuum pressure of 10⁻¹ to 10⁻³ mbar (compared to atmospheric 1013 mbar). This nearly eliminates conductive and convective heat transfer through the gap — making it 2–3× more insulating than conventional gas-filled DGU at a fraction of the thickness.
Vacuum eliminates both convection and conduction through the interspace gas. Heat can only transfer via radiation (blocked by Low-E coatings) and through the micro-pillar spacers — reducing total heat loss dramatically.
The vacuum gap is only 0.1–0.3 mm (vs 12–16 mm for gas-filled DGU). Total unit thickness can be as slim as 8 mm, enabling retrofitting into existing single-glazed frames.
Tiny stainless steel or fused silica pillars (~0.3–0.5 mm dia, ~20–40 mm pitch) support the glass panes against atmospheric pressure (~10 tonnes/m²), preventing collapse while minimizing thermal bridging.
A solder-glass or metal indium seal runs the perimeter, maintaining vacuum integrity for the 25–30 year design life. This is the most technically challenging component of a VIG unit.
Cross-section of a Vacuum DGU with Low-E coating — showing each functional layer.
Float glass (typically 4–6 mm) is cut to size, edges ground and polished. Glass must be free of surface defects. Tempered or heat-strengthened options require processing before coating as tempering must occur after cutting.
Soft-coat (MSVD — Magnetron Sputtered Vacuum Deposition) or hard-coat (CVD — Chemical Vapour Deposition) Low-E layers applied. Soft coats must face the vacuum cavity (position 2 or 3) to protect from oxidation. Emissivity ε typically 0.02–0.05.
Stainless steel, fused silica, or alumina pillars (dia. 0.3–0.5 mm, height 0.1–0.3 mm) placed on one pane in a regular grid pattern (20–40 mm pitch) using robotic pick-and-place or screen printing. Pillar density must balance structural support vs. thermal bridging.
Solder glass frit paste applied to perimeter of one pane. Both panes assembled with precise alignment. Unit loaded into furnace; frit fired at 450–500°C to form hermetic glass-to-glass bond. Alternatively, indium or tin alloy metal seals used for lower-temperature processing.
Barium, zeolite, or activated carbon getter material placed inside the unit near the pump-out port. Getter is activated during/after sealing to absorb residual gas molecules (H₂O, CO₂, N₂) released over the product's life, maintaining vacuum integrity.
Sealed unit connected to turbomolecular pump via pump-out port. Air evacuated in stages to 10⁻¹ → 10⁻³ mbar over several hours at elevated temperature (bake-out at 200–300°C) to outgas pane surfaces. Critical step determining long-term performance.
While still under vacuum, pump-out tube cold-welded or solder-sealed to permanently trap the vacuum. Port typically a small tubulation (3–5 mm dia) on the edge or face of the unit.
Units inspected for visual defects (pillar visibility, edge seal quality). U-value tested per ASTM C1363/C518. Vacuum integrity verified by thermal imaging or pressure measurement. Accelerated weathering tests per ASTM E2190. Units that pass shipped with traceability documentation.
Key ASTM standards governing the manufacturing, performance, and testing of Vacuum IGU and conventional DGU units.
Primary durability standard for IGU/DGU. Covers edge seal performance, fogging/dew-point resistance, and 25-year service life criteria via accelerated aging tests.
Defines quality requirements for the glass substrate — including allowable inclusions, surface defects, flatness, and optical distortion tolerances for float glass used in VIG.
Covers heat-strengthened (2× annealed strength) and fully tempered glass (4× strength). Critical for VIG as panes must withstand atmospheric pressure differential forces on the edge seal.
Hot Box method for measuring center-of-glass U-value, SHGC, and overall fenestration thermal transmittance. Reference method for whole-window U-value certification.
Measures thermal conductivity of flat slab specimens. Used for center-of-glass U-factor determination of VIG panels as a faster alternative to hot box at laboratory scale.
Cyclic temperature and humidity exposure to simulate 10+ years of weathering. Units must pass fogging/dew-point criteria at conclusion. Part of E2190 compliance protocol.
Classifies IGU by performance level (Class A, B, C) based on cyclic thermal exposure, high humidity, and UV radiation resistance. VIG typically targets Class A (highest) rating.
Structural load resistance of glass — including wind, snow, and atmospheric pressure loads. Particularly relevant for VIG as panes must resist ~1 kgf/cm² atmospheric pressure over the vacuum cavity.
Specifies optical and physical properties of Low-E coatings on glass. Includes adhesion, abrasion resistance, humidity resistance, and acid resistance for both pyrolytic (hard-coat) and MSVD (soft-coat) types.
Spectrophotometric measurement of solar optical properties (VT, SHGC, SC). Required for characterizing Low-E coatings used in VIG and reporting energy performance data per NFRC protocols.
Covers hybrid glazing constructions. Referenced for safety glazing laminate combinations sometimes used as outer pane in VIG to add impact resistance without full temper requirement.
Emerging ASTM method (under development) specifically for verifying vacuum pressure retention in VIG units using deflection measurement, thermal imaging, or pressure-decay approaches over accelerated test periods.
| Parameter | Vacuum DGU (VIG) | Argon-Filled DGU | Air-Filled DGU | ASTM Ref. |
|---|---|---|---|---|
| Gap Medium | Vacuum (~10⁻³ mbar) | Argon gas (90%+) | Dry air | — |
| Gap Thickness | 0.1–0.3 mm | 12–16 mm | 12–16 mm | C1036 |
| Total Unit Thickness | 8–12 mm | 24–32 mm | 24–32 mm | — |
| Center-of-Glass U-Value | 0.3–0.8 W/m²K | 1.0–1.4 W/m²K | 2.6–2.8 W/m²K | C1363 / C518 |
| Whole-Window U-Value | 0.4–1.0 W/m²K | 1.2–1.8 W/m²K | 2.4–3.0 W/m²K | C1363 |
| R-Value (centre glass) | R-12 to R-20 | R-5 to R-7 | R-1.8 to R-2 | C518 |
| Heat Transfer Mode Eliminated | Conduction + Convection | Convection only | Neither | — |
| Weight (4+gap+4 config) | ~20 kg/m² | ~25 kg/m² | ~25 kg/m² | — |
| Retrofit Compatible | Yes (slim profile) | Limited | No | — |
| Edge Seal Type | Solder glass / Indium | Dual organic sealant | Dual organic sealant | E2190 / E774 |
| Durability / Lifespan | 25–30 yr (seal dependent) | 25–30 yr | 20–25 yr | E2190 / E773 |
| Sound Insulation (Rw) | ~32–35 dB | ~34–38 dB | ~32–36 dB | — |
| Condensation Risk (inner surface) | Very Low | Low–Medium | High | — |
| SHGC (with Low-E) | 0.17–0.32 | 0.24–0.40 | 0.55–0.65 | E903 |
| Manufacturing Complexity | Very High | Medium | Low | — |
| Relative Cost | 3–5× standard DGU | 1.3–1.6× air DGU | Base cost | — |
| Tempering Required | Recommended (HS/FT) | Optional | Optional | C1048 |
| Durability Test Standard | E2190 / F3057 (emerging) | E2190 / E774 | E2190 / E774 | E773 |
U-value (W/m²K) measures heat transfer — lower is better insulation. Tested per ASTM C1363 (Hot Box) and ASTM C518 (Heat Flow Meter).
Yes — and highly recommended. Low-E coatings reduce radiation-based heat transfer, which becomes the dominant heat loss pathway once vacuum eliminates conduction and convection. The combination delivers the industry's best U-values.
| Configuration | U-Value (W/m²K) | SHGC | VLT (%) | Best For |
|---|---|---|---|---|
| VIG — Clear glass, no coating | 0.6–0.8 | 0.55–0.65 | 80–82% | Temperate climates |
| VIG + Hard-Coat Low-E (ε=0.18) | 0.4–0.6 | 0.30–0.45 | 70–76% | Moderate insulation, retrofit |
| VIG + Soft-Coat Low-E (ε=0.04) | 0.2–0.4 | 0.17–0.32 | 65–72% | Cold climates, Passivhaus |
| VIG + Dual Low-E (both surfaces) | ≤0.2 | 0.10–0.20 | 55–65% | Arctic / ultra-low energy buildings |
Metered-cabinet hot box measures total heat flow through specimen. Gold standard for U-value. Specimen size typically 1.2 × 1.5 m. Measures centre-of-glass AND edge effects.
Smaller, faster lab measurement of thermal conductivity on plate specimens. Uses calibrated heat flux transducers at top and bottom. Good for R&D screening of VIG prototypes.
Unit exposed to accelerated temperature cycling then chilled to test dew-point. Fog or frost inside unit indicates seal failure. Pass/fail criterion for ASTM E774 Class certification.
Units subjected to 10 cycles from −18°C to +60°C over 7 days, followed by high-humidity exposure and UV radiation. Simulates 10+ years of climate stress on edge seals and vacuum integrity.
Spectrophotometer measures transmittance and reflectance across solar spectrum (250–2500 nm) to calculate SHGC, VLT, and SC. Essential for Low-E coated VIG units.
Glass pane load resistance to wind pressure, snow loads, and permanent atmospheric pressure differential (~1 bar) on the vacuum cavity. Critical safety test unique to VIG vs standard DGU.
Pane deflection method: atmospheric pressure bows VIG panes inward slightly. Deflection measurement confirms vacuum level. Alternatively, helium leak detection or thermal imaging used to identify seal defects.
Acoustic performance measured in reverberation room using 1/3-octave band sound source. STC and OITC ratings determined. VIG slightly inferior to thick gas-filled DGU due to thin pane resonance.
Safety glazing impact test (for tempered/laminated VIG configurations). Ball drop and soft-body impact test. Required if VIG used in safety glazing applications per building codes.
Frame/sealant system water tightness when VIG is installed in fenestration. Tests edge seal integrity under rain exposure conditions. Relevant for solder-glass edge seal durability assessment.
| ASTM Code | Scope | Applies To VIG? | Category | Key Parameter Measured |
|---|---|---|---|---|
| C1036 | Flat glass specification | Yes | Manufacturing | Glass quality, optical distortion |
| C1048 | Heat-treated flat glass | Yes (recommended) | Manufacturing | Strength, temper level |
| C1376 | Pyrolytic & MSVD coatings | Yes (Low-E) | Manufacturing | Emissivity, adhesion, durability |
| C1349 | Clad laminated glass | Some configs | Manufacturing | Laminate bond integrity |
| E2190 | IGU durability specification | Yes (primary) | Mfg + Testing | 25-yr seal performance |
| E774 | IGU classification (Class A/B/C) | Yes | Mfg + Testing | Performance class rating |
| C1363 | Hot Box thermal performance | Yes | Testing | U-value, SHGC (whole window) |
| C518 | Heat Flow Meter method | Yes | Testing | Center-of-glass U-factor |
| E773 | Accelerated weathering — IGU | Yes | Testing | Dew point, fogging resistance |
| E903 | Solar transmittance / reflectance | Yes (Low-E) | Testing | SHGC, VLT, SC |
| E1300 | Glass load resistance | Yes (critical) | Testing | Structural safety under pressure |
| E90 | Sound transmission loss | Yes | Testing | STC / OITC ratings |
| E330 | Structural performance — curtain wall | When in frames | Testing | Wind load deflection |
| E331 | Water penetration resistance | When installed | Testing | Edge seal water tightness |
| F3057 | VIG vacuum integrity test | Yes (VIG-specific) | Testing | Vacuum pressure retention |