Wood is a hydroscopic material, which means that it has the ability to remove water from the surrounding air until it reaches a moisture equilibrium with the air. If the wood has a greater amount of moisture than the surrounding air, then it will give up that moisture until it reaches a moisture equilibrium with the air. The moisture content of wood attains when in an environment of constant temperature and humidity is termed equilibrium moisture content (EMC). The EMC of wood is typically predicted by measuring the air temperature and humidity and determining the EMC based on data for sitka. An EMC chart is presented in the Wood Handbook in Table 4-2 (http://www.fpl.fs.fed.us/) . There are also sorption isoltherms (equations) that predict EMC based on air temperature and relative humidity.
