A small angle neutron scattering (SANS) contrast variation study was performed to investigate the presence of air filled voids in fully hydrated Tencel(R) cellulose fibres. The data indicate that there are very few, if any, air filled voids within the water swollen fibres. A three phase scattering power analysis together with additional information from water inbibtion measurements show that the volume fraction of air filled voids in water swollen Tencel fibres is probably zero, but has an upper limit of 0.02. In a complementary experiment, a H2O/D2O mixture was prepared with the same neutron scattering length density as air. The difference between the SANS patterns from air and water swollen fibres persists when the fibres are swollen in an air/water contrast matched H2O/D2O mixture. The data qualitatively agrees with the analysis of time resolved SAXS data which indicated that the void size increases on drying, and the void volume fraction decreases on drying water swollen Tencel fibres (Crawshaw J, Cameron RE. Polymer, in press, Crawshaw J. PhD thesis. Changes in cellulose microstructure during processing. University of Cambridge, 1997).