Want to make one? Here's how I did it.
I cut one 5.5 x 11 inch rectangle and two 5.5 x 4 inch rectangles. I don't know much about fleece, but mine only stretched in one direction. I cut my pieces so the 11" and 4" inch sides were the lengths that would stretch. (Does that make any sense?)
I pinned my smaller pieces onto the bigger piece lining up the ends. I don't really think this is necessary because the fabric didn't move around much once I put the pieces together, but it only took about two seconds to do so better safe than sorry.
I sewed a 1/4" seam around three sides of the smaller pieces, leaving the middle open.
I turned it inside out. I would say right side out, but I don't think there is really a right side. I didn't worry about turning under any of the raw edges because it won't fray and really, I'm using it on the floor, it doesn't need to look too pretty.
I put it on my Swiffer and now I'm ready to clean!
I like how it turned out. My somewhat Type A personality wishes I used a white fleece to be able to see all the dirt it is picking up, but I didn't have any white fleece so the green will have to work.