The filter helps to prevent dirt and debris from clogging the drainage system. NDS Catch Basin Filter is removable and cleanable making it easy to maintain. It contains a Bypass feature that allows water to flow to the catch basin even if the filter is full or after a heavy stormwater event. The filter comes pre-assembled, making it easy to install: unscrew the grate, drop the filter in and reinstall the grate. The filter bag is made out of nonwoven spunbond polypropylene geotextile fabric that provides superior filtration, is inert to biological degradation and is resistant to naturally encountered chemicals, alkalis and acids. This filter bag can hold up to 40 lbs without tearing and is uv resistant. The NDS Catch Basin filter is also available for the 12" NDS Catch Basin.