Moisture is the most important factor in wood shrinkage, swelling and
warping. When the moisture content of wood rises, it swells. It shrinks
when wood moisture content drops. This phenomenon is most significant
in the directions perpendicular to the wood grain. Along the wood grain it
is negligible. Because this product has a plywood base, in which the
layers are perpendicular to each other, it is much less subject to swelling
and shrinkage than solid wood boards. Nevertheless, large changes in
wood moisture content can lead to cracks in and gaps between boards.

It is important, that the subfloor is and remains dry, that when cleaning
the floor a minimum of water is used, (use a damp cloth; never a wet
one) and that the air moisture content (relative humidity) is not subject to
large fluctuations. The relative humidity must be between 40 and 60%.