All paper stocks are hygroscopic -- that is they readily take up and maintain moisture.  Since paper is manufactured with water, they are affected by it throughout the printing process.  Whenever temperatures and humidity change dramatically enough, paper stocks will either dry up or absorb moisture.  This may ultimately affect how the sheet runs through the press.  Changes will include stretching, shrinking, waving and curling.  Planning your print jobs carefully will allow The Printing Source time to order and warehouse the paper within our facility long enough to give the stock time to acclimate to the humidity and temperature of the pressroom and avoid potential problems.