Spec sheets for reflective films arrive in a mix of American, European and textile units. Getting one wrong by a factor of 25 is easy. Here is the short version buyers need.
Thickness: mil and micron
A mil is one thousandth of an inch, about 25.4 microns. A micron (µm) is one thousandth of a millimetre. Metallised PET film is commonly quoted in microns in Asia and Europe and in mil in North America. Do not confuse mil with millimetre: 1 mil is 0.0254 mm.
Foil laminates are usually described by the thickness of the aluminium layer alone, in microns, plus the carrier. A “7 µm foil” means the metal is seven microns thick; the whole laminate is thicker.
Weight: gsm
Grams per square metre is the weight of one square metre of the finished material. It is the best single number for comparing two laminates of the same construction, because it captures foil, adhesive and carrier together. For woven laminates it is a better guide to durability than any thickness figure.
Woven scrim: denier and D-numbers
Denier is a textile unit: the weight in grams of 9,000 metres of yarn. A higher denier means a thicker yarn. The “600D” or “210D” you see on reflective fabric refers to the yarn in the woven scrim, not to the film. It is a rough guide to tear strength and hand, but two 600D fabrics can differ a lot depending on weave density, so ask for gsm as well.
Reflectivity and emissivity
Reflectivity is the share of light or heat a surface bounces back, quoted as a percentage; it depends on wavelength and on how it was measured. Emissivity is the share of heat a surface radiates compared to a perfect black body, from 0 to 1; a low number is good for insulation. A material can have high visible reflectivity and mediocre emissivity, so ask for the figure that matches the job: reflectivity for lighting, emissivity for insulation.
Quick conversions
- 1 mil = 25.4 µm; 1 µm = 0.0394 mil
- 100 µm = 0.1 mm
- gsm × 1.0 = g/m²; ounces per square yard × 33.9 = gsm
What to put on a purchase order
Construction name, film thickness in µm, scrim denier if woven, total gsm, roll width in mm, roll length in m, face colours, and the standard for any fire or emissivity claim. With those on paper, two factories will quote the same thing. Send us your spec and we will confirm the equivalent construction.