This is quite a simple pattern of single crochets and increases worked in the round.

I think you should need about 2-3 balls of normal string. Yes the kind you tie parcels with! This translates as I think an aran cotton yarn althought the stifffness of the string helps with the shaping of the hat.

You will also need less than one 50g skein of sport weight cotton yarn for the band.

This is my first attempt at writing out a pattern. Please be kind with the comments! I am happy to clarify anything that is confusing.

ETA: Some people have found that this hat works out very small I think this is because of the way I previously described the gauge. Please work the first five rounds. The diameter of this should be around 3.5inches. I hope that helps.