Topic summary
Lightweight diving helmet

Extracted from the Wikipedia article Diving helmet.
Lightweight demand helmets
The lightweight diving helmet is a type which is fitted more closely to the diver's head, reducing the interior volume, and thereby reducing the displaced volume of the helmet, so less mass is required to make the helmet's buoyancy neutral. The consequence is a reduced overall mass for the equipment carried by the diver, who must not be buoyant in the water. This reduction in volume and mass allows the diver to more safely support the helmet on the head and neck when out of the water, so when it is immersed and neutrally buoyant, it is comfortable to move around with the head, allowing the diver to use neck movement to change the direction of view, which in turn increases the diver's total field of vision while working. Since the lightweight helmet can be supported by the head and neck, it can be sealed to the neck, using a neck dam, independent of the diving suit, making operations equally convenient with dry suits and wetsuits, including hot water suits. Some models can be sealed directly to a dry suit for maximum isolation from the environment.