Definition
A thin polyester sheet applied to existing glass to add solar heat rejection, UV blocking, privacy, security, or decorative effects without replacing the window.
Window film is a thin polyester (PET) laminate — typically 1 to 4 mils thick — applied directly to the interior surface of existing glass. It is one of the most cost-effective window upgrades available, capable of providing significant solar heat rejection, UV blocking, and glare reduction without the expense of window replacement. High-security versions can also delay forced entry and reduce glass fragmentation on impact.
Types of Window Film
- Solar control film — reduces solar heat gain (SHGC equivalent reduction of 30–70%) and visible glare. Can be reflective (mirror-like exterior appearance) or neutral (less visible). Best for east, west, and south windows with summer overheating.
- Low-E film — adds an infrared-reflecting coating similar to Low-E glass coatings. Improves U-factor by 10–25%. Most cost-effective thermal retrofit for single-pane windows.
- UV-blocking film — blocks 99%+ of UV radiation, protecting furnishings, flooring, and artwork from fading. Most window films include UV blocking regardless of type.
- Safety/security film — thick (4–8 mil) film that holds glass fragments together on impact, slowing forced entry and reducing injury from accidental breakage.
- Privacy film — one-way mirror, frosted, or decorative patterns; blocks view from outside while allowing some light transmission.
- Insulating bubble film (temporary) — adhesive-free film for seasonal use; significant draft reduction; low cost; removes in spring.
Performance vs. IGU Replacement
Window film improves existing glass performance, but cannot match a new quality IGU. Low-E film on single pane raises effective R-value from R-1 to approximately R-2 — still far below a double-pane IGU at R-3.3 to R-4. Film is the right choice when windows are otherwise in good condition and full replacement cannot be justified economically.
Application and Cost
Professional installation: $5–$12 per square foot depending on film type. A typical double-hung window (15 sq ft of glass) costs $75–$180 professionally installed. Most quality films carry 10–15 year manufacturer warranties. DIY kits are available but professional installation provides better adhesion and eliminates bubbles and creases.
