Light to heavy weight knit fabric with 30%+ stretch. Jersey, French Terry, large loop terry, rib knit, sweater knit. For less stretchy fabric, use a coordinating ribbing for the neckband.
View C (Funnel Neck): Mid-weight to heavier weight knits with a bit of structure. This will help the funnel neck stand up. A stretch interfacing in the funnel neck can also add structure.
Optional: 1 yd clear elastic. (For very stretchy knits, clear elastic stabilises the shoulder seam.)