The fold or hinge on a spa cover determines what side you will open the spa cover from. Even if your spa is circle or square, the fold direction can matter. You will want to consider things like where deck railings or buildings are in relation to the spa, where the control panel for your spa is located, and if you will be using a cover lifter.
All of these considerations come down to making sure you can easily access opening and closing your cover. We recommend standing in front of your spa where you want it to open. Think of the fold like a finish line right in front of you.