Pre-Filter - For All GDP IntakesFor: GDP26000FD GDP26000F & GDPF GDPFD We wanted to give our customers a way to add even more filtration for their GDP Intake Kit, and at the same time dress it up a bit. So we decided to offer a custom made filter wrap (or filter sock), that slides over the S&B filter to give it an even more custom look. At the same time it helps keep more debris out, while still breathing good.