I just went and bought 1/4 yd. of 15 diff fabrics to make these!
I've used one of those handheld lighters that you sort of hold like a gun and has a long barrel thing, and they work well, but I went and bought a heat tool like this http://www.joann.com/joann/catalog.jsp?CATID=cat2907&PRODID=prd20134
and just put a small rock in the center of the petal to keep it from blowing away, and it works well because I don't have to worry about burning myself. I just put the petal on a piece of marble I had, then put the rock on the petal and heat away! Works really well!