Does propylene glycol provide two-way humidity control?

No. Propylene glycol (P-G) does not provide two-way humidity control. The resultant humidity from P-G is dependent on whatever the ratio of water to P-G is at that specific moment in time. If the ratio is perfect for a given temperature, it will maintain the humidity at about 70%. However, it does not react to the environment like 2-way humidity control does. To meet the definition of two-way humidity control, the technology must be able to CONTROL its environment – rather than be DEPENDENT ON its environment. The ONLY technology in the world that fits this definition is a saturated solution, which is the foundation of Humidipak’s Bóveda product. All other products, including propylene glycol, clay, desiccants, silica gel and silica beads are one-way humidifiers because the resultant level of humidity inside the humidor depends on the ambient temperature and humidity.  more