Good efficiency of fibrous filters requires not only single fibre collision efficiency but also single fibre adhesion efficiency. Especially at higher filtration velocities (>0.5 m/s) and for larger particles (>5 mu m), particles may not adhere to the fibres after impact but rebound off the fibres. The particle bounce mechanisms on filter fibres are rarely investigated, particularly for biological particles (fungal spores, pollen) which are in the size range where particle bounce is dominant. With a special measuring device working with a modified optical particle counter, single fibre collection efficiencies could be determined for various biological and non-biological particles and fibre materials. The results reveal that the single fibre collection efficiencies for biological and non-biological materials are very similar and increase with increasing Stokes number to a maximum value of about 0.45. Beyond a Stokes number of about 2, the single fibre collection efficiency decreases with increasing Stokes number, indicating particles bouncing oft the fibres, A comparison of the experimentally determined collection efficiencies with published theoretical considerations showed insufficient agreement, suggesting that the properties of the particle materials do not significantly affect the adhesion efficiency. Based on the experimental results, a mathematical correlation for the single fibre collection efficiency was derived which allows a more accurate prediction of the collection efficiency of fibrous filters.