Q: Is MDF more or less stable than solid wood?

A: This is a good question and the answer is both yes and no. Let's look at this more closely.

If an MDF panel is wetted with liquid water, extreme swelling in thickness can be encountered - up to 25 percent increase in thickness. Certainly, with MDF, it is prudent to avoid liquid water wetting. Solid wood might swell as much as 8 percent when exposed to liquid water.

Considering just relative humidity (RH) changes, if the RH varies from 35 to 85 percent, the change in size (width and length) for MDF is about 1/2 percent. The value varies with adhesive content, board density and board thickness.

For solid wood, the change for the same RH change would typically be 1 to 3 percent in width, depending on species and grain orientation. The change in length for solid wood, however, would be almost 0 percent.

If MDF stability is a critical concern, I urge you to contact the Composite Panel Association (they cover both particleboard and MDF) at www.pbmdf.com. They have some excellent publications and can provide additional technical guidance.