The Air Force puts vacuum packed bags in some survival kits. The only one I ever got to open had been packed for about 1 year. The insulation was compressed down to about the thinkness of a good blanket. After several hours it expanded to about 1 inch thickness..not real good.

Teacher has the right idea, store it as loose as possible. Some outdoor stores sell bags just for this. I have never had a Wiggys bag, so they may be different. I do remember the Air Force bag had a down fill.