The is a hand-held protective cover from anything falling from above, like rain, snowfall or strong sunlight. When not in use it has best to be compact and not obstructive. For that purpose folding or collapsible construction is preferred. Modern umbrellas have improved framing structure to achieve best portability and take least space for storing. Many use modern water-repellant materials.
The expansion and contraction, jabara function is also in use here.