How exactly are they waterproof? What happens when they get wet from basement moisture? Like after a heavy rain?

Our 5/8" Eco-Soft Carpet Tiles are not waterproof, but they are water resistant. If there is a minor flooding event, all you have to do is remove the tiles and place them outside so that they can air dry. If there is a major flooring event with sitting water over several days, the tiles may get damaged beyond repair. These tiles are made of foam, so they will float and could be salvaged by allowing the tiles to air dry and cleaning them properly. These tiles are mold and mildew resistant.