The Rubbermaid 1784122 filtration bottle filter refill 2 pack fits in the Rubbermaid filter fresh bottle. The filter takes the chlorine out of tap water on the way out of the bottle as you drink, so the water is always fresh and tastes great. The filter can be used up to 100 times before it needs to be replaced. The filter is ready to go out of the box. The on board dial on the filter helps you keep track of the amount of uses so you know when it is time to replace it. When it is time to put a replacement filter in, simply remove the bottle top, pull the old filter out and drop a new one into the top of the bottle. The ring around the top of the filter will rest snuggly into the neck of the bottle and filter the water as you drink it.