There are fabrics that are mold/mildew resistant and water reistance that you can buy. Online, look for "indoor-outdoor fabric." Joann's has some Christopher Lowell and Waverly (I think) I/O fabrics in stock. I bought some for about $8 yd at a local decorator fabric store. A big name in this type of fabric is "Sunbrella." I found from my reading that you should use bonded batting around the cushions before covering. Other kinds of batting shift and bunch up. I was going to get my batting at a local decorator fabric shop, but found it was cheaper if I bought it from an upholsterer. I hope this helps.
Whatever fabric you decide to go with, scotchguard it before you start using the cushions. They will repel any moisture and will help reduce fading also. I think Joann Fabrics has a fairly good selection of upholstery fabrics. I say go with whatever you love. Are you doing it yourself ?
