Wood acts like a sponge. It expands in the presence of excess moisture, and contracts when that moisture is given up to a dryer environment. It is always trying to achieve a balance with the prevailing relative humidity. In the Northeast, the natural seasonal swings in relative humidity are wide, and will stress the wood at each extreme. All wood responds in the same way, no matter how it’s mixed, shaved, turned it into powder and glued back together again (like the cores of plastic laminate flooring), wood will react dimensionally to the presence or absence of moisture. Wood flooring is the most stable between 35% and 65% relative humidity, the same range comfortable for people, pets, plants and other living things. Here in New England, even though human activity adds moisture to the air, it is important to humidify your home during the heating season.