I was quite pleased as this is another hurdle that i have gone through.
Now I had my three components, I cut the prefelt in a half and placed the sample for the bodice above the first half of the prefelt and the other sample of muka on the side. then i placed the other prefelt half on top of this and pinned the muka samples to the wool so they would not move in the felting process (see photos below). i also measured them so i could work out if I would get less shrinkage from a prefelt. It worked really well as you can see in the two photos on the right.
Prefelts - lay the wool, just like you do for felting and you can have two or three layers of wool (remember to lay each layer in opposing directons). I used two layers. wet with warm soapy water and roll for 150 times to 200, i did it for 150 times. I dried mine to use when I had my smples completed. You may use them wet, but it may be hard on your scissors when cutting. If you are not using your prefelts straight away, you want to wahs it so the soap does not damage the fibre. To do this roll it in netting and wash. prefelts are ususally used to put designs on your felt.