Dampits can be a safe way to humidify your cello when room and case humidifiers are not an option. A dampit has a sponge core covered with perforated tubing. After moistening, make sure it is not dripping before you insert it through the f-hole. Moisture will slowly evaporate and be absorbed into your cello. Unfortunately, the black button you see on the outside gives no indication whether the dampit is still moise or bone dry so set a schedule to refill, and stick to it until your weather changes.