I saw a similar Swiffer type duster replacement on Etsy. I thought I could make one of my own, so I did, only a little differently. All it is, is four layers of fleece, 4" x 9". Find the center and mark a line 1 1/2" from bottom x 6" long. Measure out 3/4" to the right and mark a line the same length, then measure out 3/4" to the left and mark a line the same length. Sew along these three lines. These will create your two channels for the fork of the Swiffer handle to slip into. With a sharp scissor, cut a slit about 1 3/4" from bottom, parallel to the bottom, into each channel, through two of the four layers. This will open the channel for the fork to slip into. Then, as in making a rag blanket, cut 1/2" slits all the way around the duster. Throw in the washer and dryer to fluff up. I may be mistaken, but I think using fabric softener makes these better able to attract dust. I like that it's washable, sturdy, and very inexpensive to make. Fleece is always on sale and I happened to get 1 1/2 yards in the remnant bin at Wal-Mart for about $3.00.
What I'm currently knitting is a market bag, similar to the one featured on Knitty, however, I will be knitting it in one piece, including the handles. Picture to follow, whenever it's done.