4" x 12" 100 Micron Felt Filter Sock
100 Micron Filtration - filters better but you will have to change them more often. Crystal clear water!
Standard 4 inch ring - made of high quality thick plastic unlike other socks that use inferior plastics. Fits all 4" filter sock holders.
Polyester Felt material - using felt as a filter sock material has it's advantages such as removing micro bubbles from your overflow. Micro bubbles won't pass through the felt material as they would a mesh material.