The main components of a retractable folding umbrella are a fan, support frame (strut), handle, cylinder (lock button part) that can move along the long pole, and rope that binds the umbrella body.

    Fan parabola: rainwater hits the fan surface, and the rainwater will flow down the fan surface, which is the so-called streamlined design;

    The opening of the fan surface is very large: the opening of the umbrella should be at least larger than the body width of a person so as to block the rainwater, but the opening must be large because the rainwater on the fan surface does a parabolic motion-the drop diameter formed by the rainwater on the fan surface will become larger and larger- The diameter of the ground reaches the maximum. At first, if the diameter of the parabola is large, the diameter of the rainwater will be larger after reaching the ground. In this way, people are covered by the big bell-shaped rain curtain and cannot splash or splash rainwater. On the contrary, if the opening is small, the rainwater falling on the ground will easily splash on the body or the umbrella will get rained by a little deviation.

    The umbrella with a foldable fan and a retractable shaft can keep out the rain by elongating the shaft and propping up the fan. When not in use, the fan is folded and the shaft is shortened to achieve a small and regular shape, which is easy to carry and store.