What is a cause of weakening in natural fiber ropes?

Mildew is indeed a significant cause of weakening in natural fiber ropes. Natural fibers, such as those derived from plants, are organic materials that can absorb moisture. When these ropes are exposed to damp environments and not allowed to dry properly, they become susceptible to mildew and mold growth. This biological degradation can severely compromise the structural integrity of the fibers, leading to a reduction in strength and durability over time.

Natural fiber ropes can retain moisture and provide an environment conducive to the growth of mildew, which feeds on the organic material of the fiber. The presence of mildew can cause the fibers to break down, leading to fraying or even total failure of the rope when under load.

While other factors, like storage conditions against metal or wood, can also affect the durability and lifespan of ropes, mildew specifically refers to a biological factor that directly relates to the natural fibers' composition and moisture retention properties.