We've unpacked a lot of base layers and wetsuits for the cold months.
Thermalite - lighter base layer made from lightweight polypropylene that wicks away moisture and retains body heat. Use not just for kiteboarding, but skiing, snowboarding, really any winter sports where warmth while sweating is needed.
Thermabase - a thciker base layer constructed from .5mm neoprene and Titanium lining that reflects heat back to your body. Best for watersports because of the neoprene layer.