Weakening of a rug's pile and foundation caused by prolonged exposure to high humidity or damp conditions. Moisture working into the natural fibers leaves them frail and can eventually make them decay, and the same dampness attracts moths and other pests. Damp, hot or poorly ventilated storage, bathrooms and humid climates are the usual settings; remedies are a dehumidifier, good airflow, a rug pad that blocks moisture rising from the floor, a lower pile that absorbs less humidity, and airing the rug outdoors in the sun for a few hours once or twice a year, without leaving its face in strong sun for long. Humidity swings also make a wool foundation stretch and shrink and distort the rug, whereas a cotton foundation holds its size better.