Loom: a 1/2, 3/8 small, 3/8 fine or 1/4 fine gauge loom that allows you to knit in the round, large enough to make a cowl with the circumference you desire.
Yarn: weight appropriate to your loom, but a firm fabric is best. Suggested weights and amounts:
Caron Cakes aran: 1/2 inch gauge or 3/8 small gauge (1 skein) Premier Sweet Roll aran: 1/2 gauge or 3/8 small gauge (2 skeins) Lion Brand Ice Cream sport: 3/8 small, 3/8 fine or 1/4 inch fine gauge (1 - 1.5 skeins)