Optical preforms and methods for forming optical preforms are disclosed. According to one embodiment, a method for producing an optical preform includes compressing silica-based glass soot to form a porous optical preform comprising a soot compact. The porous optical preform is heated to a dwell temperature greater than or equal to 100° C. Thereafter, the porous optical preform is humidified at the dwell temperature in a water-containing atmosphere having a dew point greater than or equal to 30° C. to form a humidified porous optical preform. The soot compact portion of the humidified porous optical preform generally comprises greater than or equal to 0.5 wt. % water.