Every two years, the members of the association carry out an interlaboratory comparison of the analytical performances of their laboratories. The laboratories involved are most generally the central laboratory of these companies but, when appropriate, external laboratories used by the members are also involved.

The exercise is focusing on the chemical analysis of the nine main parameters used for characterising feldspar products, which are at the basis of the EUROFEL common terminology:

Na₂ O / K₂ O / CaO / Al₂ O₃ / Si O₂ / Fe₂ O₃ / Ti O₂ / Mg O / Loss on ignition.

Each participating laboratory feeds in the exercise two different samples of commercial ungrounded product. A 300 g batch of each sample is provided to each of the participants, as well as to the EUROFEL Secretariat, for archival purpose. The selection of these samples is left entirely up to the participants, assuring that the widest possible range of feldspatic products is indeed considered (from feldspatic sand to high grade feldspar). For the preparation of these samples and batches, standardised practices (e.g. quartering etc.) are applied.

No standard analysis method is imposed; the participating laboratories analyse the sample according to the methods they routinely apply.

The results are plotted on a graph with sample identification as abscissa and weight percentage as ordinate.

Although it has no absolute value, a "EUROFEL concentration" is also calculated for each element, by averaging the individual results. If one result appears to significantly divert from the bulk of the analysis, it is omitted from the calculation of the average value and of the standard deviation. Should this "outsider" be eventually in the range of the average value + 5 standard deviation, it is included in the final calculation of the average.