Thermal modification uses heat to remove some natural compounds within wood;
Water from being absorbed,
Nourishment for fungi & insects.
Leaving the treated lumber more stable; meaning product is less susceptible to cupping or warping.
In Depth: Thermal modification works primarily on the supporting material in the cells walls, also known as hemicellulose.
By slowly heating the wood for a number of hours, with the absence of oxygen; the hemicellulose will lessen and most of the water will be forced out of the wood. Creating a stronger bond between the wood cells themselves.
Density Decreases- Without losing too much strength or structure