Storing either one compressed or even stuffed in a small sack is a bad idea. Most good sleeping bags include a big cotton storage bag for that reason. Of course, hanging fully lofted in a closet or something would be best but most folks don't have room for that.
My gear is banished to my storage shed out back. I'm sure the heat isn't good for it but I store everything loose in big laundry bags or in large rubbermaid bins. This keeps the lizards and bugs out of them (I hope). So far so good but I think my oldest bag at the moment is only about 5 years old.
Good luck and don't store your insulation compressed if there's any way to prevent it.