Good discussion of humidity with water vapor/temp table that I came across:
Humidity
Cigars should be stored in an environment that permits the cigar to be smoked at its best. Many authors have suggested that this "ideal" environment be around 70 ºF with a relative humidity of 70%. If a cigar is too dry, it will smoke hot, fast and unevenly. If a cigar is too moist, it will tend to go out frequently, draw will become harder, and it runs the risk of molding in storage. Either of these extremes is undesirable.
Thus, it is recommended that cigars are stored in humidors (boxes that are designed to maintain a constant environment for cigars to rest) to maintain them in peak condition for smoking.
Humidors range from inexpensive containers with humidification devices to works of art that showcase the wood workers' skills and cost multiple thousands of dollars. Which one is best? - If the humidity and temperature is controlled appropriately, either the budget version or the "break the bank" version will perform equally well.
The one thing both humidors have in common is that they contain a regulation device to control the humidity inside the storage container at a given temperature. These devices range in complexity from low-tech (a sponge soaked in water at the bottom of the humidor or brass containers with a clay substance to hold moisture and release moisture i.e. the Dunhill system) to devices that use blotting paper to hold and release moisture. Low-tech devices often require the owner to adjust the humidification device to maintain the desired humidification.
Another device, thought to be one of the best, is the Credo System (registered trademark). The Credo System comes in both a small model (the Rondo) capable of handling 25 - 50 cigars, and the larger model, the Precision 70 which is capable of handling 75 - 100 cigars. Obviously, for larger storage requirements, multiple Credo units can be used.
The beauty of the Credo System is that it is self-regulating. All you have to do is add distilled water to keep the device saturated, and it will maintain a constant 70% relative humidity at 70 ºF. This is accomplished by using special "Credo Solution", which contains both distilled water and a "tensio-active" agent. The tensio-active agent releases moisture when the RH is too low, and absorbs moisture when the RH is too high. It has been determined that the "tensio-active" agent in the Credo units is nothing more or less than propylene glycol, and the units come pre-charged with this agent. You then add distilled water until the unit is saturated with water, and install in your storage. After several months, Credo recommends that you "recharge" your unit with "Credo Juice" (which is for all intents and purposes a 50-50 mix of propylene glycol), due to the fact that the tensio-active agent is slowly consumed when in use.
Many cigar smokers have begun to make their own humidification devices based on this information. Sponges are commonly used to hold propylene glycol and distilled water, but a better choice appears to be the green foam used by florists in flower arrangements (brand name is OASIS). OASIS is available from your local florist and often from craft shops. A large brick of this foam is enough to make a number of humidifiers and can be purchased for a very affordable sum. The foam is soaked with propylene glycol, distilled water is added until the foam will no longer accept any more distilled water. This is then placed (in an appropriate ventilated container) into the storage container, to maintain the cigars in peak condition.
Although humidity levels are almost always referred in terms of Relative Humidity, the actual value that is important is the amount of water vapor present in a given volume of air, known as Absolute Humidity. As air will hold varying amounts of water vapor at different temperatures, no discussion
of humidification would be complete without a discussion of temperature and it's effect on absolute humidity. Relative humidity is an easily measured value that relates the measured humidity to the maximum humidity that is possible at that temperature. Thus, 70% RH at 70 ºF is not the same as 70% RH at 80 ºF.
We are aiming to maintain the same amount of water (mgm/liter) around our cigars as seen at 70% RH at 70 degrees F (which is 13.15 mmHg water vapor pressure).
So, to be able to know what is happening with our cigars at temperatures other than 70 degrees F, we must use a table of adjusted relative humidity values to make sure that our humidors keep our cigars in the peak of condition.
Temperature, water vapor pressure and relative humidity required to equal 70% RH at 70 degrees (13.15mmHg).
Temp
Water Vapor Pressure
Relative Humidity
66
16.37
80.33%
67
16.95
77.58%
68
17.55
74.93%
69
18.17
72.37%
70
18.79
70.00%
71
19.45
67.61%
72
20.11
65.39%
73
20.81
63.19%
74
21.51
61.13%
75
22.25
59.10%
76
23.00
57.17%
It is not possible to attain an absolute humidity level that will keep cigars from drying out at temperatures below 60 degrees F. This observation will put to rest the fallacy that the refrigerator is a good place to store cigars. Not only do we have to worry about our premium cigars beginning to acquire the flavors from left over foods but the cigars will dry out and become essentially unsmokable. The freezer is an even worse place to store cigars. The humidity becomes virtually zero, and the loss of moisture from cigars will accelerate to produce a bone-dry smoke.
