The 2 mm wetsuit hood from the Isurus Evade range.  It will keep you warmer than other 3 mm hoods.

The Isurus Evade wetsuit hood is made from Ti-Z Fleece insulated Yamamoto neoprene. It's impenetrable to wind, exceptionally comfortable and reduces stress on the head and neck. You’ll find the Isurus wetsuit hood to be the thinnest, warmest and most comfortable surfing hood you have ever worn.