The umbrella column is a sturdy 3.5 inch aluminum extrusion that has internal channels to allow the umbrella to be wired for heating or misting. Horizon umbrellas are designed to withstand strong winds, and are intended to remain open while in use, and are locked in place using a through bolt. This waterproof umbrella can be closed however it takes approximately 15-20 minutes to close the umbrella for the season. This model is perfect for seasonal applications where our customers are looking to open their umbrella prior to the beginning of their seasonal use, then leave them open for the entire duration of their season. The most common use for this model of umbrella is at pool areas where the customer will install their Horizon umbrella prior to Memorial Day weekend, then retract the umbrella when its time to close their pool area for the year.