Any fleece or wool is great for this neck warmer. We especially recommend Polartec Powerstretch for a lightweight warmer or 200 weight for a heavier one.
Size S or M is good for stretchy fleeces, but when using a non-stretch material size L is recommended. The stretch of the fleece should be along the length of the warmer (so it stretches over your head).
The warmer can optionally be made with stretch cording in the upper edge's hem. Stretch cording along with a cord lock allow you to adjust how tight the warmer is around your chin. It can then also be worn as a hat by closing the hole.
1 cm seam allowances are included in the pattern. A normal sewing machine is fine for this project, but a serger can be handy for the edge seam and finishing the bottom edge.