in an atmosphere of steam. The relative humidity of the steam was regulated by controlling the dry-bulb temperature and maintaining a wet-bulb temperature at the boiling temperature of water (212° F.). The method is applicable to 1-inch Douglas-fir, true firs, western hemlock, ponderosa pine,
southern yellow pine, basswood, and sapwood of sweetgum. 

So far as is known, it is not suitable for other hardwoods or for softwoods that have a tendency to collapse. While the reduction in drying time was well worthwhile, the severe drying conditions
caused such rapid deterioration of materials used in kiln construction that the use of superheated-steam kilns was discontinued in the United States.