The most frequently used product in fast-food restaurants that is also the most frequently used marketing surface. Paper trays are ususally thrown away after use, hence its material has not to be special. In terms of price-value ratio the best choice is the paper cut to rectangular shape, but any custom die-cut shapes are also available.
If the plate coasters are not intended to be thrown away after use, printable plastic materials can be chosen as well. By rounding-off corners, sharp edges can be avoided.