This is the HEPA filter for the full size Simplicity canister models, S30, S36, S36L, S38, S38L. If your Simplicity has a lower model number then these, THIS WILL NOT FIT your model. This filter is located on the top of the vacuum cleaner. You can find this filter by finding where the air is being exhausted. Simply pull the tab for the filter cover, and remove the filter cover. All Simplicity models using this filter will have a filter change indicator located on the handle of the hose. When this indicator turns on, it's time to replace the filter. Also when changing this filter, you will need to push the filter reset button located right next to the filter underneath the filter cover.