Why is there a flat round spot on the corner of my REEF inflatable mat?

This is normal, all of our mats have this feature. This is located on the side opposite of the valve and is created because the drop-stitch strings that attach one surface to the other are not able to be utilized where the plastic valve is located. This is something that is inherent to drop-stitch construction and will not compromise the integrity of the mat. Check out a video of this below.

REEF Mat // Construction Overview Video: