Shells and Trellis was the first pattern ever donated to Halos of Hope, by our dear friend, Melody Hamor. Variations of this hat have been made mostly with remnants of fibers from other (larger) projects. We have seen it in worsted weight, DK and with 2 sock yarns held together. It's an incredibly popular hat according to the cancer centers. After you've made it once or twice, you'll easily go back to it again and again.
Several hook sizes are suggested, given variety of fibers suggested.