Hi,
The Whites MK0 and MK1 are designed to be layerd with either the MK2 or MK3 undergarment system.
The MK0 is a full body bamboo fiber undergarment that is designed to be worn against the divers body. Bamboo fiber is naturally moisture wicking, anti-microbial, and eco freindly. The MK0 has no thermal properties alone, but can significantly reduce the chilling effect of sweat on a divers body by wicking it away from the surface of his skin.
The MK1 is designed to be worn by itself in very warm water or as a first layer in very cold water to add extra thermal protection. It is constructed of super stretch fleece,and provides a full body form fit which reduces the rate of heat loss in critical areas such as the crotch and armpits. In the tropics the MK1 would be the ideal undergarment to wear with your Fusion.
The MK2 is a 2 piece undergamrment system (jacket and john) designed for mid range water temperatures. The thermal properties of the MK2 can be greatly increased by layering the MK1 beneath it.
For the coldest water, the MK3 Primaloft undergarment is the best choice. It is a single piece undergarment with nylon on the exterior, fleece on the inside, and a layer of Primaloft insulation sandwhiched in between.
Let em know if you have any further questions.
Cheers,
Justin Balaski