ECE 104 is the European regulation that defines the technical requirements of retroreflective materials used on trucks and trailers driving in Europe. That includes vehicles of category M2, M3, N, O2, O3 and O4.
The regulation with amendments made in 2015 distinguishes between material class C to F:
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The requirements a material needs to fulfil in its respective material class in order to be approved are specified with regard to size, coefficient of retroreflection, colour and resistance to external elements. ECE-104-approved materials show an approval mark with the letter “E” in a circle and furthermore the number of the state where it was approved, the material class and the approval number.
ECE 104 does not include information on the actual application of the reflective materials. The application of conspicuity tape that is used for contour marking on large and heavy motor vehicles (ECE 104 class C) e.g., is specified in ECE Regulation
Find more information about contour marking according to ECE 104 and ECE 48 in our blog post on 
Conspicuity Tape
