Wood is a hygroscopic and porous dielectric medium, which means that fresh,
undried wood has both free and bound water within the solid matrix. Free water
can appear as vapour or liquid in the pores. Wood with mc below the fibre
saturation point contains mainly bound water captured in the cell matrix structure.
If the mc is above the fibre saturation point during the absorption of
electromagnetic energy, the temperature of the wet wood piece will reach the
boiling point of water. As the temperature increases, the internal pressure will also
increase, causing moisture evaporation that will be forced from the interior
towards the surfaces of the wood piece. How fast the vapour will be transported
from the wood piece depends on the wood structure, i.e., how large the wood
voids are, how they are connected and how much energy is needed to release the
bound water in the wood cell structure.