In order to store thermoplastic preforms in a container, the outside faces of the preforms are treated so as to make said outside faces more slippery, and the preforms are stored in bulk in the container, with the outside faces of the preforms after treatment presenting a coefficient of friction that is low enough to ensure that the packing density, i.e. the number of preforms stored per unit volume, is greater than the packing density that would be obtained under the same conditions with non-treated preforms.