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Recent developments in making fibre materials using the foam‐forming technology have raised a need to characterize the porous structure at low material density. In order to find an effective choice among all structure‐characterization methods, both two‐dimensional and three‐dimensional techniques were used to explore the porous structure of foam‐formed samples made with two different types of cellulose fibre. These techniques included X‐ray microtomography, scanning electron microscopy, light microscopy, direct surface imaging using a CCD camera and mercury intrusion porosimetry. The mean pore radius for a varying type of fibre and for varying foam properties was described similarly by all imaging methods. X‐ray microtomography provided the most extensive information about the sheet structure, and showed more pronounced effects of varying foam properties than the two‐dimensional imaging …