Which material is primarily designed for ring buoy life lines due to its light weight and floating characteristics?

The material most commonly used for ring buoy life lines is polypropylene. This is due to its advantageous properties that align with the requirements for safety equipment used in marine environments. Polypropylene is lightweight and exhibits excellent buoyancy, which means it can float on water without submerging. This characteristic is vital for life lines, as they need to remain on the surface for quick retrieval during emergencies.

When considering the other materials: nylon, while strong and durable, tends to absorb water and can become heavy, diminishing its floating capability. Polyethylene, though it does have some floating characteristics, does not typically provide the same strength and flexibility required for life lines compared to polypropylene. Canvas is fabric-based and, although durable, does not float and is not suitable for life lines in life-saving applications. Thus, polypropylene's unique combination of lightweight and buoyant features makes it the ideal choice for this purpose.