It looks like fondant ribbon to me. I have a large island in my kitchen, so I roll it out on that.
I googled the cake in it said white ribbon & white flower.
Actually you can buy ready to roll fondant ribbon I believe. I think I've seen it somewhere. But if I were you, I would roll it myself in a long counter or table.
I have a Wilton Ribbon cutting tool that I use. I start with a fondant 'snake' and roll it out flat. Then I take my ribbon cutter and make a few ribbons. Gently roll the ribbon up like you would roll up that bubble tape gum kids chew. Know what I mean? Then place the roll of 'tape' against the bottom of the cake and gently unroll next to the cake. This keeps from stretching the 'ribbon' out of shape by picking it up. Makes it much easier to move when it's rolled up.
I agree about rolling it up like the bubble gum tape is the easiest way, just make sure that you have it dusted well with cornstarch or Pwd sugar or it will all stick together and you'll have to start all over!
Thanks everyone for the help
Who did that beautiful cake? You should always post your source to give credit to the person who did the cake.