A portable humidifier and a method of using the same. The portable humidifier has a frame; a fluid droplet generator on the frame; and a fluid containment unit for a supply of fluid. The fluid droplet generator is operable to cause fluid droplets generated from fluid from the supply in the fluid containment unit to become entrained in environmental air in a space in which the portable humidifier is located. The fluid containment unit has a wall structure that is selectively reconfigurable to occupy different surrounding volumes.