Introduction: Helium-3 was used for comparison of NMR measurement of gas diffusion along different directions within nanoporous ordered Al2O3 aerogels at room temperature in Paris and low temperature in Kazan [1,2]. Aim: This work aimed at a test of the validity and limit of the Knudsen model of gas diffusion within native and compressed aerogel samples [2] for a wide range of gas densities and associated mean free paths. Methods: At 300K, 10-30 mbar of laser-polarised 3He gas mixed with 0-1 bar of N2 (effective pressure Peff=10-2500 mbar) was used for multiple (CPMG or XY-16 sequences) spin-echo studies at 2.6 mT with pulsed gradients G of fixed or variable directions and strengths. At 4.2 K, diffusion was probed at 0.5 T with Boltzmann polarised 3He gas (10-1000mbar), Hahn-echoes, and static gradients. Results: Within aerogel, diffusion was strongly restricted at all gas densities and a “free diffusion regime” was achieved (negligible effects of sample boundaries). At 300 K, 3He polarisation (∼50%) typically yielded SNRs around 200. Diffusion anisotropy (changes in apparent diffusion coefficient Dapp with the angle between G and aerogel fibers) was highest at low Peff (up to a factor of 2). At 4.2K, we have observed that the degree of diffusion anisotropy depends significantly on the aerogel porosity, notably in the compressed samples. We have also observed a strong decrease of gas diffusion and a deviation from the expected Knudsen) behaviour, attributed to the low-T enhanced influence of the walls attractive potential on gas dynamics. Discussion: Our measurements of anisotropy and pressure dependence of Dapp at 300 K support and complemented the 4.2 K findings. They significantly extend the range of gas densities used to probe restricted gas diffusion in such complex materials. [1] anr.fr/Projet-ANR-19-CE30-0023; RSF project: 20-42-09023 [2] Kuzmin et al. (2023) doi.org/10.1021/acs.jpcb.2c08251