I bought some cotton and some silk, along with some netting, in the local craft store. Cotton was to test the method, the silk was for the actual shawls. I didn't realize until I tried the test scarves that the cotton I'd bought, while it was the correct open weave style and able to be felted, was in fact iron-on interfacing and therefore not useful for felting. The interfacing caused a blockage and attempting to felt gorgeous wool onto that just didn't work. I tried tossing it into the washer with the towels I was washing to see if that'd make it work better. It didn't:
First off, I laid out my bubble wrap and the silk on top of it, to measure out the area and make sure I had enough bubble wrap.
To finish, rinse the soap out with cold water to shock it into a bit of a stronger felt, then crinkle it up into a ball and throw it against a surface (like the bathtub bottom) a few times until it feels as stiff and has wrinkled up the way you'd like it. After rolling it will still be flat, but some of the appeal of Nuno felting is the wrinkles the felted bits give to the open silk. Roughing it up after rinsing out the soapy water gives it those wrinkles.