Which option is NOT a characteristic of vinyl ester resins?

Vinyl ester resins are a specialized type of thermosetting resin that offer a variety of advantageous properties for composite materials, particularly in marine and industrial applications. The characteristics of vinyl ester resins typically include good hydrolytic stability, excellent impact resistance, and superior fatigue resistance.

Good hydrolytic stability means that these resins can withstand long-term exposure to water without degrading, making them suitable for applications where moisture resistance is critical. Excellent impact resistance allows the material to absorb energy from impacts without failing, which is important for durability. Superior fatigue resistance enables the material to endure repeated stress cycles without breaking down over time.

However, high flexibility is not a prominent characteristic of vinyl ester resins. While they do offer some degree of flexibility, they are generally stiffer and less flexible compared to other types of resins, such as polyurethanes. This lack of high flexibility makes the correct response valid since it highlights a property that is not typically associated with vinyl ester resins.