The invention provides a diameter reducing system for reducing the diameter of a flexible container as the container is filled. The system includes a stretching device to stretch the container at the fill level as the container is filled with a plurality of particles. The stretching device can release a stretched portion of the container substantially at the fill level as the fill level rises. The container can be a flexible, elastic bag. Shrinking of the container at the fill level as the container fills promotes supporting engagement between particles to enhance the structural integrity of the filled container and to reduce the likelihood that particles will be damaged during movement of the filled container.