The Pentair Pentek GAC-20BB Big Blue Carbon Water Filter 20″ Replacement 4 Pack is a set of four 20″ water filters designed for home use. These filters are made with activated carbon and are certified by NSF for quality assurance. With a size of 4.5″D x 4.5″W x 20″H, these filters are easy to install and are effective in reducing chlorine and other impurities from your water. The blue color and sleek design make them a stylish addition to any kitchen or utility room. Made by the trusted brand Pentek, these filters are a reliable and efficient solution for clean and safe drinking water.