For two very different reasons: stickiness versus speed. Surfboards are (usually) made of fiberglass, which gets slippery when wet. A layer of sticky wax – often mixed with a little sand – creates some traction on top of the board, making it easier for surfers to paddle, pop up, and scoot around without slipping overboard. Snowboarders (and skiers), on the other hand, apply wax to the bottoms of their boards to create a waterproof barrier. This barrier reduces friction between the board and the snow, boosting speed and improving control for sick tricks in the terrain park.
Picture Credit : Google