The sample hat was made with worsted weight wool but you needn’t stick to that. In fact I wouldn’t have stipulated it if the Ravelry form didn’t require it. You can use any yarn you like (lace weight might not be your best choice for warmth…) and any size needles. It’s the particular construction that allows for this.

In worsted weight on size 7 US (4.5 mm) or 8 US (5.00 mm) needles, this is a very entertaining two-night project. You may never look at making a hat the same way again :)