: I have heard that two layers of 4oz glass, on the hull would be stronger and
: add less weight to the boat than one layer of 6oz glass.
: Is this due to the 6oz glass wicking more epoxy?

Stronger yes, lighter no. Just due to the fact that there is more glass in 2 layers of 4 ounce means it will be stronger than one layer of 6. But 2 layers of 4 ounce has the potential in a well produced layup of being stronger and lighter than one layer of 8 ounce. The finer weave can result in a higher glass to resin ratio which means less resin and less weight. The finer weave also means the fibers will tend to be straighter. Also two layers can be set at an angle to each other so the strength will be more evenly distributed in all directions.

However, two layers are harder to lay up than one, an there is a risk of ending up with more resin than necessary which makes the lay up heavy, or air trapped between the layers which makes it weaker.