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 and pattern, 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.
Roll dimensions
Width is quoted in millimetres across most of Asia and Europe and in inches in North America, and the two appear on the same enquiry more often than you would expect. Length follows the same split, metres against yards, where one yard is 0.9144 metres. Core diameter is quoted in inches almost everywhere, even on otherwise metric spec sheets.
Price units: per linear metre or per square metre
These two are not comparable until you know the roll width behind them, and the gap is large enough to decide a tender. At 1.50 m wide, a price of one unit per linear metre is two thirds of a unit per m²; at 0.75 m the same headline figure is one and a third units per m². Divide by the width the price is quoted at — not the width you want — before comparing two suppliers. Our own indicative bands are quoted per linear metre for this reason, with the basis stated.
Which of these numbers actually predicts anything
Weight predicts more than thickness, and construction predicts more than either. A gsm figure captures film, adhesive and carrier together, so two laminates at the same gsm are carrying a similar amount of material. Thickness can be inflated by a deep emboss that adds caliper without adding substance, which is why a finished thickness quoted against one pattern does not transfer to another.
Denier predicts least of the three. It describes one yarn in the scrim and says nothing about weave density, yarn construction or the film face, which is why two fabrics sold honestly as 600D can differ widely.
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 a spec sheet that lists all of those, two factories will quote the same thing. Send us your spec and we will confirm the equivalent construction.