Dinged U.S. Foam Board

I smashed up my fish that was made with U.S. Foam and something interesting happened. It seemed not to take on any water. I’ve been doing ding repair for the past year and most of the boards with that kind of damage would be soaked. The board was in the water for about 20 minutes after the damage but left in my car for about 5 hours after that happened. Just wondering if anyone else has similar or contradicting experience with U.S. Foam.