The white material on the outside is called a pre filter. It grabs all the bigger particles of crap before they even get to the filter which helps the carbon last longer.
The pre filter needs to be cleaned roughly every 4 weeks, I've heard taking it off and vacuuming it out of the grow space is the way to go, not washing it as it can get damaged and then it can't be used again until it is 100% dry as well.
Going to hook mine up for the first time maybe today or tomorrow. Walked through the back laundry door last night when I got home from work & the first thing I could smell was the girls. Strange since they're not even 3 weeks old and haven't begun to auto or show pre flowers (well no preflowers when I watered yesterday morning anyway)