Excellent heat retention. Easy to get on and off.

The high degree of blood circulation through the head means you can suffer substantial heat loss when the head is exposed to ambient water.
Even a warm wetsuit or drysuit will lose half of its heat retention capacity (especially in cold water) if the head is uncovered. This is why a hood is an extremely effective way of retaining extra heat.
Take this opportunity to feel the difference in warmth for yourself.

Silver Ti Coatedskin

Thermal insulation:
Dual-action heat retention keeps you comfortably warm by sticking close to your skin to trap the water warmed up by your body heat and by creating a thermos-like insulation effect via the metal coating.

Comfort:
High water repellency speeds up the drying process and keeps you comfortable when putting your gear back on for the second dive of the day. This reduces the unpleasant chill you get when wet fabric touches your skin.

Details
Smooth skin piping fits tightly around the face and inhibits water intrusion.
Any air that collects in the hood from exhalation or other sources is expelled via the top of the hood. This prevents hood misalignment.
The zipper slider is made by YKK for maximum reliability.
A zipper barrier makes it easy to get the wetsuit on and off, minimizes water intrusion, and keeps your hair from getting tangled in the zipper.