RapidPure Explorer Camp Housing Extension adds length to the filters that reduce bacteria and cysts. RapidPure captures viruses that are too small for other filtration systems to capture. The Explorer Camp Housing Extension is an added feature of the best in class RapidPure water purification system. The housing extension comes in 3 different sizes depending on your specific trip or activity: standard size, one-3.5in extension, and two-4.5in extensions.