I always use 2 layers of Vilene and have been happy with the results.

I always use 2 layers and the FSL have been perfect.

i like to use two.

I also use 2 find that works for me!

I use two layers, the top placed at right angles to the bottom, and very often I sandwich WSS scraps in between just as big as the design will be. I did a WorkAlong with Phil from Bargain Embroidery and she advised me to use three layers. I've had success with every FSL design I've stitched. If you want the finished item softer, then soak it for longer to remove all of the WSS. Some smaller items are nicer if they are stiffer - not soaked so long - like ornaments or jewellery.
Everyone has their favourite method. Just watch the stitchout to make sure that a very dense design is staying flat, nice and smooth. You'll work out what your machine likes to use best and the best of luck to you. FSL is the greatest fun!!!
AlmaG.

I always use 2 layers of Vilene (fiber like) wss.

Dawn, by now - you have stitched out your 1st FSL design - how did it go? *4U