A working humidor has three components: an airtight Spanish-cedar-lined enclosure, a calibrated hygrometer, and a humidification source. Everything else (lacquered finishes, glass tops, dividers, brand badges) is comfort, not function.
The enclosure can be a traditional desktop humidor (a wooden box lined with Spanish cedar) or a tupperdor (a food-grade airtight plastic container with cedar trays inside). Both work. The traditional humidor looks better and ages well; the tupperdor is more forgiving in dry climates and cheaper to scale up. The non-negotiable is the airtight seal; a humidor that leaks cannot hold its conditions, no matter how good its other components are.
The hygrometer must be digital and calibrated. Analog gauges drift over time and most ship from the factory two or three percentage points off. Calibrate using the Boveda one-step calibration kit (a small pack that holds at seventy-five percent for testing purposes), or with the salt test (a sealed environment with saturated salt slurry, which holds at seventy-five percent at room temperature).
The humidification source for most users is a Boveda pack at sixty-five or sixty-nine percent, sized to the volume of the humidor. Two-way packs absorb and release moisture as needed and last several months before drying out. Older crystal-gel humidification systems work but require active management; Boveda is the easier choice for new owners.
For more on humidity targets and stability, see How to Rest a Cigar.