Heat Rejection Window Film Guide

Heat Rejection Window Film Guide

Heat rejection is one of the most cited benefits of smart film — and one of the most prone to exaggerated or unverifiable claims. This guide explains how PDLC and SPD film reject infrared heat, what the verified performance numbers are, and what those numbers actually mean for comfort and energy use in your space.

How Smart Film Rejects Heat

Smart film rejects heat primarily by blocking infrared (IR) radiation from sunlight. IR radiation is the portion of the solar spectrum that carries heat energy — it is why sunlight feels warm on your skin even though visible light does not.

• PDLC film (frosted/OFF state): The randomly oriented liquid crystal droplets scatter and absorb IR radiation. ElevatoX PDLC film rejects up to 77% of IR in the frosted state, depending on model.
• PDLC film (clear/ON state): When the crystals align, IR rejection drops significantly because light (including IR) passes through more easily. IR rejection in the clear state is about 10–15%.
• SPD film (dark/OFF state): Suspended particles absorb visible light and IR. SPD film rejects up to 60% of IR in the dark state, with ≥ 82% UV rejection (ON) and ≤ 96% UV rejection (OFF). Adhesive-type SPD achieves up to 99% UV rejection in both states.
• SPD film (clear/ON state): IR rejection is about 14% in the clear state, while visible light transmission is ≥ 60%.

Verified Performance Data

These numbers are derived from elevatoX product documentation and test reports. The key insight: maximum heat rejection occurs in the privacy (OFF) state, which is exactly when you want it most — during peak sunlight when the room is unoccupied or when you need glare and heat reduction.

What Heat Rejection Actually Does for Comfort

IR rejection reduces the solar heat gain through glass, which directly affects indoor temperature and cooling load:

• Reduced radiant heat: Less IR passing through the glass means less radiant heat hitting occupants and surfaces near windows.
• Lower cooling load: With less solar heat entering the space, air conditioning systems work less to maintain the target temperature.
• Glare reduction: The frosted state also reduces visible light transmission, which cuts glare on screens and work surfaces.

Important: we do not publish specific energy savings percentages (e.g., "save 30% on cooling") because actual savings depend on building orientation, local climate, window area ratio, existing HVAC efficiency, and occupancy patterns. Any specific percentage claim without a site-specific energy model is unreliable.

Common Pitfalls and Misleading Claims

• "Smart film cuts cooling bills by X%": This claim is unverifiable without a building-specific energy model. The actual savings depend on too many variables to quote a single percentage.
• "SPD film is more energy-efficient than PDLC": Both consume approximately the same power in the ON state (3.7 vs 3 W/m²). SPD achieves lower VLT in the OFF state (≤ 2% vs ~27%), which blocks more total solar energy, but the IR rejection mechanism is different, not necessarily more efficient.
• Confusing UV rejection with heat rejection: UV rejection protects furnishings from fading but contributes minimally to cooling load reduction. IR rejection is the primary driver of heat gain reduction.
• Ignoring clear-state performance: Smart film is clear for most of the day in many applications. Clear-state IR rejection (10–15%) is much lower than frosted-state (up to 77%). The benefit is concentrated in the hours when the film is in privacy mode.

FAQ

Does smart film reduce room temperature? Smart film reduces solar heat gain through glass, which reduces the cooling load on air conditioning. The actual temperature reduction depends on window area, orientation, and climate. The primary benefit is comfort near sun-facing windows, not whole-room temperature change.

Which is better for heat rejection — PDLC or SPD? SPD film achieves lower VLT in the OFF state (≤ 2%), blocking more total solar energy. PDLC film achieves higher IR rejection percentages (up to 77%) but in the frosted state only. For applications where deep tint is acceptable, SPD provides stronger overall solar control. For privacy-focused applications where you still want some daylight, PDLC is the better choice.

Can smart film replace air conditioning? No. Smart film reduces solar heat gain, which reduces cooling load. It does not produce cooling. It is a supplement to, not a replacement for, HVAC systems.

What about electrochromic film for heat rejection? Electrochromic film changes its tint gradually over seconds to minutes, providing variable solar control. However, we do not publish electrochromic performance specifications because specific brand data is not publicly verifiable. General characteristics include low steady-state power and slow transition speed.

Next Steps

Review PDLC model specifications on the product page, compare all parameters on the specifications page, and request a quote for your project. Use the wiring simulator to plan transformer and control layout.