: Liquid water doesn't penetrate polyester resin. The microscopic tubes and
: pinholes created by the evaporation of the solvents used in the making of
: the resin are too tiny for a water molecule to penetrate. Only molecules
: of water vapor are small enough to get through, and it takes a good long
: time under normal weather conditions.

The styrene in polyester resin exaporates through the partially cured resin, causing molecule-size wormholes through the film. Depending on the cure stage, these wormholes may be partially or fully developed. Styrene is a fairly large molecule, having a molecular weight of 104.15 (http://www.jtbaker.com/msds/s6986.htm). Water is one of the smallest molecules around, just 2 atoms of hydrogen and one of oxygen, with a molecular weight of 18.02 (http://www.jtbaker.com/msds/w0600.htm). That is so regardless of the phase, whether liquid, solid or gas. Water in any of its phases can easily pass through a styrene-size wormhole. Surface tension comes into play, but the molecule size does not change.

The proof of this is that fiberglass boats decay over time. Blowboaters talk about hulls "going soft", or losing stiffness. Water does penetrate polyester over time, causing degradation of physical characteristics. Whether this is caused by permeation through the wormholes or through microfractures of the gelcoat is a matter of some controversy, but at the end of the day the exact mechanism doesn't really matter.

Does any of this make any difference to the paddle? Probably not. The polyester is plenty good. Just wanted to set the chemical record straight.