sun reflective window films

Typical sun reflective window films are "retrofit" products, that is, sheets to be applied to the glass of low-performance windows. Their goal is to reflect the sun's heat, keeping it outside.

What are sun reflective window films?
In their simplest and most typical presentation, home window films are polyester sheets with a scratch resistant coating and an adhesive, applied to the interior surface of the glass panes.

Uses of Sun reflective window films

Typical window films are best used in hot or moderate climates with long cooling seasons, to keep the sun’s heat outside.

But there are now some window films that may also help reduce heat loss to the outside, but this feature remains largely unconsidered in common residential uses… Window films are mostly used as a mean to block the sun’s heat, reflecting solar radiation back from the windows.

Solar Films limitations

Common window films are of little or no use in cold climates. They block the sun's heat in the winter (and not only in the summer), and that's a big disadvantage in cold climates.

The energy-efficiency of reflective window films depends a lot not on climate and long cooling seasons but also on the size of window (they lose efficiency in large glazing areas) and on window orientation (see Window Orientation , below).

Types of window films

Mirror-like films (sun reflective window silver films) are usually more effective than the other more transparent and colored films.

Visible Transmittance

Pay attention to the VT (visible transmittance) issue. Sun reflective window films can cause loss of natural lighting. To avoid or minimize it you should choose a window film with a high VT coefficient, that is, as close to 1 as possible.

See: Windows Ratings

SHGC window film coefficient

The energy efficiency of sun reflective window films is largely expressed in their SHGC (Solar Heat Gain Coefficient). The lower the coefficient (a value between 0 and 1) the better. A very low coefficient means a very high effectiveness in blocking the sun's heat outside...

See: Windows Ratings

Window orientation

Window films are of little or no use in north-facing windows, in the northern hemisphere (or in south facing windows, in the southern hemisphere).

They are more advantageous in east and west windows, to block the glare and unwanted sun’s heat. They can also be very advantageous in south-facing windows (or the north facing windows in the southern hemisphere) to reduce air conditioning in hot climates.

Sun Reflective Window film prices and warranties

Prices between $3 and $12 per square foot of sun reflective window films are common. Warranties of 5 years are also common, but they vary with the type of film and the manufacturers.

Installation

Installing sun reflective window films is a typical DIY job.

Professional installation costs range from $1 to $5 per square foot. Some manufacturers require professional installation of their window films, but many companies promote the DIY installation.

NFRC labeling

When selecting home solar window films, prefer products with a high VT (Visual Transmittance) and a low SHGC (Solar Heat Gain Coefficient).

Both the SHGC and the VT are expressed by a value between 0 and 1. In North America, the energy performance of the window films can be assessed through the NFRC label (see below).

Alternatives to window films

Sun reflective window films can be a cheap way of getting lower cooling bills. They can be relatively efficient and cheap and easy to install.

But new energy-efficient windows (or glass doors) are a better alternative, if your are going to install new windows. See: New efficient windows.

Solar screens - made of vinyl-coated polyester, typically mounted with screws on the exterior side of the windows... - are another alternative.

Exterior overhangs, awnings, sunscreens, interior blinds and devices as shades and draperies can also be - to a certain extend - alternatives to sun reflective window films (See: Awnings, blinds...).