It will stay stiff. What brand of fusible are you using?
One way to make a fusible applique softer is to cut out the middle of the fusible shape before fusing to fabric. For this technique, you draw (the reverse shape) directly onto the fusible paper, cut out the middle leaving about 1/4" inch of fusible between the cut edge and the drawing line, then cut on the drawing line.
You might want to try Misty Fuse. This is a very lightweight fusible that gets rave reviews. It does not come with paper, so you need to use a teflon-type applique sheet or parchment paper to protect surfaces when you fuse. (It will peel right off a teflon sheet.) Here is a link to it on Amazon:
http://www.amazon.com/Mistyfuse-Mist...dp/B000PFPSJI/
Misty Fuse comes in different sizes and colors, so do a search before deciding to order.
Edit: For the most natural look to the applique, use parchment paper rather than a teflon pressing sheet. The fabric ends up with a slight sheen to it with the teflon.