Let me provide two examples: The very fine texture of a glass veil wets out incredibly fast due to the good fiber dispersion, small filament diameter and high surface of the fibers. But don’t expect the resin to move through this veil to wet out subsequent layers of reinforcement. In fact, if the resin has any entrained air, the air bubbles will likely become permanent voids in the laminate.
On the other hand, a coarse fiber CFM typically has excellent wet-through and allows resin and entrained air to quickly pass through the architecture of the mat. Individual filaments in a large bundle may wet more slowly in a coarse mat, but trapped air has a much easier time escaping the laminate structure.
In summary, so many variations in glass fiber reinforcements can affect the end product. There are plenty of ways to tune a composite to achieve the needed properties of the end user. The best strategy is to partner with material suppliers to ensure the desired results.