Swim hat so I don't turn into my mum when swimming

[MrsFogi]

As a child I used to dispair at my mother swimming without getting her hair wet. However, I'm now starting to see her point as I've started swimming a few times a week (with no swim hat) to get fit for this giving birth business but it is ruining my hair. So, is there such a thing as a swimming hat that is waterproof but doesn't give you static/frizy hair (as the plastic ones seem to). Any suggestions on how I can go swimming but not end up with staw hair gratefully received!