A spectacle frame material that is extremely lightweight, will not rust or corrode, and is superior in strength, but tends to be expensive and hard to solder is:

The correct choice, titanium, is renowned for its exceptional properties that make it a favored option for spectacle frames. Titanium is extremely lightweight, which enhances comfort for the wearer, especially during prolonged use. Its remarkable strength-to-weight ratio means that it can withstand significant stress without bending or breaking, making it suitable for durable eyewear.

Another key advantage of titanium is its inherent resistance to rust and corrosion. This is particularly beneficial in environments where moisture and humidity are present, as it helps to maintain the frame's integrity over time without the need for frequent replacement.

Despite its excellent qualities, titanium can be more expensive than other materials. This higher cost is often attributed to the complexities involved in its manufacturing and processing. Additionally, working with titanium can pose challenges, particularly when it comes to soldering, as the material can be difficult to join seamlessly, often requiring specialized techniques.

These characteristics solidify titanium's position as a premium choice for eyewear frames, particularly for those looking for a balance between functionality and aesthetic appeal.