There are two kinds of prefelt. One is needled prefelt. Commercial prefelt is done this way. It is needled just enough to hold together. I use this sometimes, it works very well. I get it in small pieces and by the yard from Dreamspin Fibers. http://www.dreamspinfibres.ca/ (shameless plug for a friend).
The second is wet felted and this is easy to make yourself. Lately that is what I have been doing. You layout your felt as usual but you stop when it is just holding together. Rinse it out carefully and let it dry. it is till fragile but strong enough to cut out shapes when you don’t want the fuzzy edges that traditional layout gives you. I have been making small pieces and some from the ends of some batts that are not big enough to do much with. They are very helpful when you want very definite shapes.
I don’t have any exact plans for them but they are very handy to have around.