The invention relates to a thermoplastic and/or elastomer composition that comprises: at least 50 wt % and 99.95 wt % at most of a starchy composition (a) including at least one starch; at least 0.05 wt % and 50 wt % at most of a nanometric product (b) including particles having at least one dimension of 0.1 to 500 nanometers and selected from mixed products containing at least one lamellar clay and at least one cationic oligomer or cationic synthetic polymer, organic, mineral or mixed nanotubes, organic, mineral or mixed nanocrystals and nanocrystallites, organic, mineral or mixed nanobeads and nanospheres customised into clusters or agglomerated, and mixtures of these nanometric products, the percentage being expressed in dry weight and added to the sum in dry weight of (a) and (b); and at least one non-starchy polymer (c).