I have a small table that I built to put on my porch. I use it mostly to put my feet up on in the summertime. It does a good job of that. I made it out of cedar for the legs and apron which I also painted. I used some thin pallet wood for the top. After I made the piece and it sat on my porch in the sun, the top cupped and stayed cupped. Then one winter we had a good snow storm. About 3 or 4 inches fell and when I went out in the morning I saw my table covered in a thick white blanket. It was very pretty. I thought nothing of it.
Later that day, since snow doesn’t stick around for long at our elevation, I looked at the table again and like magic the top boards were dead flat. All the snow had melted on top of them and they had expanded and gone flat. It was stunning the transformation from misshapen and curved to flat.
Water and wood were made for each other. In fact wood loves water. A standing tree is made up mostly of water. Which is why it’s so danged heavy. Cupping is simply caused by one face of a board being wetter or drier than the other. It moves more than the other face and movement occurs. It was fun to see this in action on my front porch. Of course by spring, the boards were cupped again but still usable as a footrest.