sentences:  These crystals should not be placed in contact with the textiles, but may be placed in breathable muslin bags and hung inside the case to maintain a constant humidity; they should be monitored periodically, however, to be sure that they are working.In areas where climate control is unavailable (such as in historic buildings), the conservator can still moderate the temperature and relative humidity through use of fans, humidifiers and dehumidifiers, and portable heating or cooling units.In addition to temperature and humidity, air flow is also a concern for textile preservation.