Dampness can cause mildew. Colors between panels can bleed on certain nylon fabrics in spinnakers and Gennakers when the sails are wet when stowed away. Roll up wet roller-furling sails loosely to promote drying. Fold sails, don't stuff. Creasing can break down fibers in the fabric and weaken the sail.
Store sails away from dampness and heat.
Never store sails in the trunk of your car. Exposure can deteriorate the adhesive bonding. Cleaning Clean every year before winter storage. Remove dirt and salt using mild detergent and brush. Avoid excessive agitation.