The following article appeared in the last issue of the Superior Thread Company Newsletter and is used with permission from Bob Purcell from Superior Threads.
How long does thread last? Is it OK to use Mom's or Grandma's thread?
Thread, like many other products, has come a long way in recent years. The last 10 years has seen more change in thread quality than at any previous time. New technology has brought about better raw material, more consistent spinning, better dyeing, and improvements in each step of the processing. Companies which apply these technologies are able to produce a far superior product than companies which choose to ignore them or cut corners. Of course it costs more to make sure each step of the process is done at the highest level which is why there remains such a wide range of quality on the market. The answer to the shelf life questions is, "It depends."
If I had some of Mom's cotton thread on the shelf, would I use it? Maybe. What about some of Grandma's cotton thread? Probably not. However, 50 or 80 years from now, I would not hesitate to use Superior's King Tut thread, which is the absolute highest grade cotton in both raw material and processing. The shelf life of today's best thread is much longer than in previous years.
Here is a way to test if old thread has deteriorated: Conduct three or four break tests. Hold a 4 to 6 inch length of thread in your hands and gradually pull apart, adding more tension to the thread until it breaks. If the thread tends to pull apart, it is weak and probably not suitable to use. If it breaks with a clean snap, it is still OK.