Bowed, But Not Broken...

Check out the photo below, showing a small sheet of 1/2" plywood sitting in the roof rack of our FJ.  I took this photo on Monday, when we were having some rain (about a tenth inch, nothing to get all that excited about).  The sheet was perfectly flat the day before, but look at it now!

The rain hitting the top side of the plywood soaked into the wood, causing it to swell a bit.  The bottom of the plywood remained dry, and therefore didn't swell.  But the swelling is directional – the fibers of wood grow in diameter, but not in length.  The grain of the top ply of this piece toward/away from the position of the camera, so the swelling occurs in the left/right direction.  This swelling caused the bowing in the direction you can see.

Later on, the water soaked down further in the wood, to the next ply.  At that point, the piece warped a bit in both directions, making a very odd-looking piece of wood.

Today (Wednesday) the piece has dried out, and is completely flat again...