Bio-based materials are increasingly recommended because they have a low environmental impact and correspond perfectly to high environment quality buildings. This article presents the moisture properties of a new bio-based material called flax lime concrete (FLC) and of hemp lime concrete (HLC), which is used to validate the experimental protocol of this work. The moisture properties (sorption isotherm, water vapor permeability, moisture diffusivity) and moisture buffer capacity estimated from the moisture buffer value were determined to gain knowledge about the behavior of these materials under equilibrium and dynamitic conditions. The results showed that both bio-based materials have high hygric performance and exhibit an "excellent" moisture buffer capacity according to the classification proposed by the Nordtest project. (C) 2014 Elsevier B.V. All rights reserved.