Which synthetic rope feature allows it not to stiffen when wet?

The feature of low moisture absorption is key to ensuring synthetic rope does not stiffen when wet. Ropes that absorb minimal moisture will maintain their flexibility because they do not swell or change shape significantly when exposed to water. This characteristic is especially important in applications where ropes may frequently encounter wet conditions, allowing for consistent performance and handling.

The other features listed, while important in their own right for different aspects of synthetic rope performance, do not directly address the issue of stiffness when wet. High tensile strength refers to the rope's ability to withstand heavy loads without breaking, which is unrelated to the rope's behavior in moisture. A hollow core design might influence the rope’s weight or buoyancy but does not directly prevent stiffening from moisture. Similarly, a high weight capacity speaks to the amount of load the rope can handle without failure, rather than its reaction to water exposure.