Glass types

Smart glass (electrochromic & switchable)

Smart glass changes its tint, opacity, or light transmission on demand, flip a switch (or let heat or sunlight do it) and the glass responds. Three different technologies sit behind that trick, each with its own strengths, failure modes, and the jobs it is actually right for.

6 min read Intermediate Emerging technology

Three switchable glazing technologies

Electrochromic (EC)
A thin-film coating on the glass changes color when a low-voltage DC current is applied. No current = clear. Current = tinted. Holds state without continuous power.
Best for: Facades, skylights, office buildings. Slow transition (1–5 min). Permanent until switched.
PDLC (Liquid Crystal)
A polymer-dispersed liquid crystal film between glass layers is clear when powered (crystals align) and frosted/opaque when unpowered (crystals scatter). Requires continuous AC power to stay clear.
Best for: Interior partitions, conference rooms, privacy on demand. Instant switching. High energy use to maintain clarity.
SPD (Suspended Particle)
Microscopic light-absorbing particles suspended in a film align when voltage is applied (clear) and randomly orient when off (dark tint). Continuously variable, any level between clear and dark.
Best for: Automotive sunroofs, skylights, atriums. Fast, continuously variable. Continuous power needed for clarity.
ELECTROCHROMIC TINT CYCLE (simulated)
Clear → tinted state transition takes 1–5 minutes in real products

Electrochromic glass in depth

Electrochromic (EC) is the smart glass you are most likely to meet on a real commercial facade. In the US the leading product is View (formerly View Glass), with competitors like Sage Electrochromics (now part of Saint-Gobain) and others.

An EC unit is a stack of ultra-thin layers on a glass substrate: an electrochromic layer (usually tungsten oxide), an ion conductor, and a counter electrode. Apply a small DC voltage (1–5V) and lithium or hydrogen ions shuffle between the layers, making the electrochromic material soak up sunlight so the glass darkens. Reverse the voltage and the ions move back, clearing it again. The clever part: it only needs a little charge to change state, and none at all to hold the tint, so it barely sips power.

Performance in tinted and clear states

PropertyClear stateTinted state (darkest)
Visible transmittance (VT)~60%~1–3%
SHGC~0.39~0.09
U-factor (typical IGU)~0.26–0.28~0.26–0.28 (unchanged)
Transition time1–5 minutes (zone size dependent)
Intermediate statesYes, continuously variable between clear and darkest
U-factor does not change
A common misconception: smart glass improves U-factor when tinted. It does not. U-factor measures conducted and convected heat flow, which is determined by the IGU construction (panes, gas fill, Low-E coating). Smart glass controls solar heat gain (SHGC) only. For winter insulation, the glass performs the same regardless of tint state.

PDLC (privacy glass) in depth

PDLC film is the magic behind "switchable privacy glass", the conference-room walls and hotel bathroom screens that snap from clear to frosted at the flick of a switch. The film holds liquid crystals floating in a polymer. Power on, and the crystals line up with the field and the film goes clear; power off, and they scatter back to random, turning the glass milky white.

Key limitations of PDLC:

  • Requires continuous power to remain clear. A power outage = instant opaque (may be desirable or undesirable depending on application).
  • Does not block solar heat gain effectively, frosted PDLC still transmits infrared radiation, making it ineffective as a solar control strategy.
  • The frosted state provides privacy but not blackout. In bright sunlight, silhouettes may still be visible through frosted PDLC.
  • Has a limited rated switching cycle life; repeated switching degrades the film over time.

When smart glass makes sense

Smart glass is not cheap, usually 3–8× the price of a standard insulated unit, so it only earns its keep in specific situations:

  • High-performance facades with dynamic solar control: EC glass can eliminate exterior shading devices (blinds, fins, louvers), freeing up facade area and simplifying maintenance. For west- and east-facing glass in hot climates, the energy savings can justify the premium over the building lifecycle.
  • Conference rooms and executive spaces: PDLC privacy glass replaces traditional blinds and provides an immediate, maintenance-free privacy solution with a clean architectural look.
  • Skylights and atrium roofs: Overhead glass must often be tinted to control solar gain and glare. EC or SPD glass allows the space to be bright on overcast days and shaded on sunny days automatically.
BAS integration required
Electrochromic glass requires integration with the building automation system (BAS) to deliver energy benefits. An EC facade operating in manual mode provides occupant comfort but not optimal energy performance. Sensor-driven automated tint control based on sun angle, irradiance, and occupancy is needed for full ROI.

Current limitations

  • Transition speed: EC glass takes 1–5 minutes to fully transition, unsuitable for applications needing instant privacy.
  • Color shift: Most EC products tint to a blue-grey hue. The color shift is visible from both inside and outside and must be accepted as part of the design intent.
  • Uniformity: Large EC panels may tint unevenly, edges may reach full tint before the center. Manufacturers mitigate this with zoned wiring patterns.
  • Long-term durability: EC and PDLC technology has improved significantly, but long-term facade durability in harsh UV and thermal cycling environments is still accumulating real-world data. Warranty terms vary significantly by manufacturer.
  • Cost: Smart glass costs $50–$150/SF installed, compared to $15–$40/SF for high-performance conventional IGU.
Disclaimer: Performance values are representative of current commercial products and will change as technology evolves. Consult the specific manufacturer for current specifications and warranty terms.