As this cowl is made with measurements, you can use any hook and any yarn you prefer.
However, the hook you use should be 2 sizes bigger than the hook you normally use with the yarn you choose. It has to be loose. If the cowl is too stiff it will not be comfortable to wear.
I normally use the 5mm with Drops Nepal, but for this cowl I used the 7mm.
I used for the cowl in the picture:
Drops Nepal, Yarn thickness group C, 50 gr = 82 yds, 10wpi
With the 7mm hook: HDC 10x10cm (4”x4”) = 9st x 10 rows
For the child size cowl as pictured:
3 skeins of the main color.
A different color for the edging.
Yarn needle to weave in ends
CH - Chain
SLST - Slip stitch
HDC - Half Double Crochet