Shrinkage and swelling happens under moisture changes.

Shrinkage is the process of reducing the size and volume of the wood due to reduced amount of water in it. Shrinkage of wood caused by content of water in the dry air, and there is process of returning to the environment of the adsorbed water from the cell walls of the wood. Thickness and size of the cell walls reduce because of disappearance of the absorbed water. Excessive shrinkage of the board may be the cause of the occurrence of cracks; shrinkage of a one side may be the reason of bending the cutting board.

Swelling is the process of increasing in size and in volume of wood due to increasing water in the wood, which depends on content of water in moist air or water.

We use 8% moisture level wood in End Grain Cutting boards manufacturing.  Under air moisture increasing wood moisture increase too, and swelling occurs; shrinkage occurs under moisture reducing. Different wood species react differently to moisture changes.

Averages changes of wood characteristics when the wood moisture from 8 to 9% and vice versa

Wood moisture changes are less than air moisture changes. The table below shows that, for example, when moisture changes from 50 to 40% at a temperature of 20 ° C (68 ° F), wood moisture reduction is 1.5%. Temperature has a much lower impact on the wood moisture. For example, increase in temperature from 20 ° C (68 ° F), to 30 ° C (86 ° F) at a relative moisture 50%, reduce the total moisture content of 0.4%.

The change in the wood moisture content in %, depending on the climatic conditions according to Calvert (the numbers in the table indicate the wood moisture content)