All my strops are 11" x 3" to fit my... wait for it... 11" x 3" strop holder. I have several 12" knives and don't think that 11" is too short. I also have a bunch of short knives and don't think 3"-- which is the standard width for Japanese stones, BTW -- is too wide.
Don't worry too much about size, as long as it's larger than 8" x 2" and fits your work area conveniently. Too wide is definitely not a problem in use, but can be a waste of stropping compound.
All of my strops are mounted and rigid. They're either leather of one sort or another, hard felt or balsa. You can use bovine or horse leather, textured or smooth. You can use the leather charged (with stropping compound) or plain (not charged).
Balsa is an excellent strop, it takes and holds a charge well, but it's easy to gouge if you're not careful. I used to use MDF and Masonite, but prefer basla.
I used to true some of my knives on plain manilla file folder paper mounted to a hard backing, but I like leather or felt better and haven't had a paper setup for some time. FWIW, ordinary newsprint works well for deburring, finishing and truing too. But felt is more efficient.
The only charge I'm currently using with my strops is water based CBN, which I get from US Products. I like it quite a bit, but don't make too much out of the "only" because I fool around a lot and will undoubtedly go back to using boron and diamond charges now and then. CBN, boron and diamond are all better than the ever-popular green chrome oxide.
Chrome oxide still has fans, but I think they're moored in the past. Not only are CBN, boron and diamond faster, but they're make for better edges as well. Chrome oxide edges lack sufficient bite for kitchen knives; and besides, chrome oxide is VERY messy. It might still be a good choice for razors, though; I couldn't say.
Diamond is very fast, but it's expensive and the edges don't hold up as well as CBN or boron. Boron compound is good, but it's slow compared to CBN and I haven't found a good inexpensive source.
My current preference is to sharpen on charged balsa and do a final polish on plain leather. I use the felt to chase the burr and help deburr difficult knives. More often though, I use plain leather to do any final chasing and polishing, then deburr with a cork, felt block, piece of softwood, or whatever. The slightest hint of compound or water wrecks a felt strop, so don't keep your station too close to the sink, and dry your knives very thoroughly after rinsing the compound.
As I said, I enjoy fooling around with strops, but...
Bottom line: Stones are better for most purposes.
Edited by boar_d_laze - 1/19/13 at 6:07pm