The definition 3mm is the "definition" Of a reliable Stay-Warm dive suit. It is built with scubapro’s body map system, a manufacturing method that uses a 3D cut, special tailoring and material inserts to create a suit that fits like a glove, provides extra stretch where it's needed most, and offers excellent warmth, comfort and durability. The infrared fleece interior lining reflects body heat to ratchet up warmth even more, Plus it's comfortable as can be against the skin. This suit offers a level of warmth and comfort any warm-water diver will love.