On those frigid, frosty mornings when most sane people wouldn't dare touch the water, let alone choose to be submerged in it for a decent length of time, you need something to keep you warm as you gear up. 20% of your body heat is lost through your head, so in cooler temperatures it is vital that you wear something over your head to retain that heat.
The Poseidon Power Stretch Hat (beanie, knitted cap, tuque, whatever you want to call it) is stylish and comfortable but most importantly will keep you warm before your dive, after your dive, and on any other occasion when a warm head is desirable.