These are devices to ensure correct process fluid distribution as well as to prevent the exit of any large solid particles from the vessel. Many reactors operate with regeneration cycles where flow reversal occurs, so the baskets are designed for two way operation.

Construction typically comprises an inner 'can' with slotted perforations to provide the correct open area, velocity and distribution profile, covered with a coarse mesh or wedge wire screen and sometimes a fine mesh filter layer, depending on the application.