A spectacle frame material that has high flexibility and will maintain the flexibility if soaked overnight periodically in water is:

The correct answer is that nylon is a spectacle frame material known for its high flexibility, especially when wet. Nylon frames can bend without breaking and can return to their original shape, making them comfortable and durable for eyewear. This flexibility is a key characteristic, as it allows the frames to be adjusted easily for a better fit and enhances their resilience against impacts and stress.

Additionally, when nylon is soaked in water, it retains this flexibility and does not become rigid or damaged, which is advantageous for prolonged use, especially in contact with moisture. This property also contributes to its suitability for active or sports eyewear, where flexibility and resilience are critical.

In contrast, while other materials like cellulose acetate and cellulose aceto-propionate may offer some level of flexibility, they do not maintain their structural integrity in the same way when exposed to water over extended periods. Optyl, while lightweight and hypoallergenic, does not possess the same level of flexibility and water resistance as nylon does.