I am considering buying a reel or two of tennis string, but it would take me many years to finish the entire reel because I would use only about 20 feet at a time in a hybrid job. If it's unused in a reel, does tennis string (either polyester, co-poly, or nylon) have a shelf life? How long would it take before its playing characteristics change--5 years, 10 years, or more? I'd like to save some money by buying an entire reel, but not if it wouldn't play as well years down the road before I finish using it.