Seal
To know whether a cigar humidor has a good seal, listen for a whooshing or puffing sound when the lid is closed. This is the sign that the humidor is sealing. If a humidor doesn't make this noise, chances are high that it's not sealing properly. This can result in dried-out cigars.
Humidity
Quality humidors keep the humidity of cigars between 65 and 75 percent. Humidity in different ranges will result in cigars that are dried out or moldy and damp.
Liner
A quality cigar humidor has a cedar, non-aromatic, kiln-dried liner. This type of wood is the best at keeping cigars from warping because it can handle the humidity. Spanish cedar is the best, as western red cedar and American cedar can affect the flavor.
Body Material
A quality humidor is made from real wood, not wood inlay. It should also have real glass instead of acrylic glass, if the humidor has a glass top. It's a given in the cigar world that if real wood and glass isn't used, the piece probably had skimpy manufacturing and it will more than likely not do the job.
Joints
Quality humidors should have dove tail or spline joints. This is the mark of expert craftsmanship.
Size
Cigar humidors should be able to contain about 50 percent more cigars than the smoker plans to store. The reason is that cigar smokers generally buy larger amounts of cigars over time as their cigar habit increases. Buying a roomy box that will allow for a growing collection is of the utmost importance. It's better to have too much room than not enough.