I went to an estate sale last year and purchased a large gallon Ziploc bag of thread. Some had been used and some not (plastic cover still on). I do the strand test with every spool before use. So far no problems. I save the those "silica" packets that come with medicine bottles. Some spools are still in the bags. I toss the little silica packets in those bags for a little safeguarding for the used spools.