Permeability plays an important role in governing the durability of concrete in deleterious environments. Previous permeability tests using water as the permeating medium have indicated that the addition of cellulose fibre is effective in reducing water permeability both in the presence and absence of stress and thereby making concrete more durable. In this paper, further evidence was sought of pore-refinement in concrete reinforced with cellulose fibre using cryoporometry (CP) and mercury intrusion porosimetry (MIP) methods. Cryoporometry was carried out using a differential scanning calorimeter (DSC). Two volume fractions - 0.1% and 0.3% - of a treated cellulose fibre were investigated. The results indicated a definite pore refinement due to cellulose fibre addition and a related improvement in durability.