Fourth Element Men's X-Core VestFourth Element Men's X Core Vest The physiological response to cold stress is to reduce blood flow to the periphery and look after the body core, where it can often just be a matter of time before cold becomes the limiting factor in the safety and enjoyment of a dive. X Core provides extreme thermal protection to the core, enabling longer, more comfortable dives. Designed to be worn under an Arctic, Arctic Expedition, Halo 3D or any other drysuit