For window film optical & thermal property testing, the window film must be applied onto a glass substrate, and it is not practical to test the window film as a standalone film.
If the objective is to obtain the performance data of the window film on a specific type of glass, the film needs to be applied to the known glass type for testing. The glass substrate could be a single glazing glass (e.g. a laminated glass) or a double-glazing unit (DGU).
If the objective is to generate the general performance data of a window film, the following glass substrates are recommended in NFRC 304:
- Applied films are measured with transparent glass with a solar transmittance greater than 0.820 (Tsol > 0.820) and a visible transmittance greater than 0.890 (Tvis > 0.890).
- Glass that meets this criterion includes 3mm clear glass, 3 mm low-iron glass, 6 mm low-iron glass.
In practice, we recommend using 3-6 mm clear or low-iron glasses as the substrate.