The climate in which a piano lives must be well regulated. Humidity levels affect moisture content in the soundboard having a direct effect on the bearing of bridges against strings, thus altering the tuning. Wool felt bushings and leathers shrink and swell, become loose or tighten, squeak and rattle, and produce more of less friction than is necessary. Warpage of parts and weakening occurs as moisture content fades. Sunlight bleaches lacquer finishes and windows provide an unseen degree of heat exchange.