By blocking the water flow between fingers and keeping them in direct contact with each other,body heat cycles from one finger into another, improving over all hand temperature and reducing claw incidences.
Why nonumb is a safe when the claw develops ?
Wetsuit swimmers, can experience the Claw syndrome but doesn't mean any other thing that cold hands. A good wetsuit should keep the body core at a safe temperature. Nonumb reduce hands heat lost, and preserves an efficient catch preventing numb fingers from spreading apart.
Swimsuit swimmers wearing nonumb will extend resistance to cold and lasting more time in the water. When The Claw starts to develops swimmers can feel the numbness even wearing nonumb, but their catch wont be compromise, allowing the swimmer to safely go back to shore, or for the extremely experience cold water swimmers to preserve a good catch.