Laceweight yarn is used doubled in this pattern.

“This makes a deep-crescent-shaped shawl that comes out as wide around at the bottom as a circle but is knit back and forth like a half circle, starting from the neck: so that when you wear it, it’s hanging straight down from the neck, not doubled over like a full circle would be. All your work shows, rather than being concealed in a doubled-over jumble (my prejudice on circular shawls.)” - from Alison’s Website.