A humidor is any kind of box or room with constant humidity (and often, temperature as well), used to store cigars. For private use, small wooden or acrylic glass humidor boxes for a few dozen cigars are appropriate, while cigar shops often have walk-in humidors, sometimes covering a whole floor. Humidors of all sizes use hygrometers to keep track of the humidity levels. The ideal humidity in a humidor is around 65-70%, with the box filled close to the rim. The more empty space exists in a humidor, the more readily the humidity will drop.
Humidors are made of Spanish-cedar wood, or plastic. Spanish-cedar is suitable for aging cigars for three reasons. It holds more moisture than most woods, so it will help maintain humidity. Second, the aroma will impart itself on the cigars if they are retained in it for long enough. That is also why some cigars are wrapped in Spanish-cedar sheets when you buy them. Tobacco blenders use this to give cigars an extra dimension in flavor.
Last, Spanish-cedar wood sometimes repels tobacco beetles, although there have been instances where the beetles have eaten through the wood. These pinhead sized beetles can ruin entire stocks of cigars. They eat the tobacco and lay eggs, causing further infestation. These beetles can also be discouraged by ensuring the humidor does not get hotter than 20°C. The beetle eggs usually only hatch at around 25 °C, although there are also instances where they will hatch at cooler temperatures if the humidity is too high.