I used silk in a quilted vest for my son--wonderful drape. I would agree with Feline that it doesn't give you the loft or quilting definition that wool does. I use wool often, usually as the top bat when I double bat to get super definition of quilting. Wool is wonderful! It needles so nicely, it's breathable so you don't sweat under it, lightweight, washable, etc. Wish I could afford to use it all the time but...
I haven't quilted it yet (cause it was expensive compared to 80/20 or even all cotton) but Hobbs as a cotton that is needle punched, no resin or scrim called Premiere that is so soft and lush--can't wait!