Nearly all modern Stand up Paddle Boards have at least 1 air vent installed on the deck. Air vents are used as a way to help prevent delamination of the epoxy resin/glass from the EPS foam blank. When delamination occurs, it creates huge air bubbles underneath the shell case. This causes the shell case to become brittle, bulge, flex and can crack when stepped on. Delamination happens when pressure builds up inside the board. Primarily, the pressure build up is caused by two things: heat and altitude changes.
Delamination by Heat
Nearly all stand up paddle boards use EPS foam cores because the material is lightweight and reasonably easy to shape. But when EPS heats up, it can become unstable and expand, causing delamination. Your SUP can warm up quickly when not in the water. Leaving a SUP exposed on the beach or shore, without a bag covering it, can cause a board to delaminate. An air vent helps prevent delamination by allowing some of the expanded gases to equalize, but it is not a cure. If you are not using your stand up paddle board, you want to keep it in the shade or secure it in a board bag.
If you are travelling on a plane, always remove the valve from the board before hand