Which type of fiber is used for high-strength lines and has been in use for a long time?

The correct answer is vegetable fiber because these fibers, such as manila and sisal, have been utilized for centuries in maritime applications due to their natural strength and durability. Vegetable fibers are derived from plant materials and have a long-standing history in the industry, providing qualities such as resistance to mildew and good tensile strength, which makes them suitable for high-strength lines. Their historical significance in rope making has established them as a traditional choice for various applications.

In contrast, while polyester and polypropylene are widely used modern synthetic fibers for lines due to their strength and resistance to environmental factors, they do not have the same historical use as vegetable fibers. Aramid fibers, known for their exceptional strength and heat resistance, are relatively newer and primarily used in specialized high-performance applications, rather than for standard high-strength lines historically associated with traditional maritime uses.