Storing in sealed plastic can damage a quilt if moisture is sealed with it. Folding isn't bad if you take it out regularly and fold it in another direction. I store mine with all my other bed linen. Used to re-use the bags I got when I bought bed spreads or mattress pads - but didn't like the smell. Some people make a "pillow case" to store it in with a bit of the fabric on the edge so they know which quilt is inside.