What defines the physical properties of a booster line?

The defining characteristic of a booster line is its diameter and rigidity. Typically, booster lines have a 1-inch diameter and are made from materials that provide a rigid structure, allowing them to maintain their shape under pressure. This rigidity is crucial because it helps in delivering water effectively during firefighting operations.

Moreover, booster lines are designed for a variety of applications, including initial attack situations where quick deployment and ease of handling are essential. Their size and construction enable them to be maneuvered easily, making them ideal for situations that require a fast response.

In contrast, other characteristics mentioned in the question do not align with the fundamental properties of booster lines. For instance, while collapsibility and being lightweight are features of certain hoses, they do not describe a booster line accurately. Additionally, booster lines are not defined by a larger diameter compared to other types of hoses, nor are they primarily used for high-pressure applications like certain fire suppression systems, which could include other hose types intended for such uses.