Approach A3 (Model Yu 1, Equation 4.9, cylinders, exp. PD, incl. wall-effect) was
closest to the experimental results; the results of approach A2 were close to that of A3.
Since all approaches underestimated the experimental packing density of mixtures 1-7,
the approach that gave the highest virtual packing density of the fibres resulted in the
best accuracy. The mean error of mixtures 1-7 was 0.018 with an average variation of
2.1% (mixtures 1-8: 0.019 and 2.3%).