The invention provides a diameter reducing system for reducing the diameter of a flexible container as the container is filled. The system includes a shrinking device to shrink the container at the fill level as the container is filled with a plurality of particles. The shrinking device can include a heater to direct heat at the fill level. The container can be a bag formed from heat shrinkable material. Shrinking of the container at the fill level as the container fills promotes supporting engagement between particles.