I am 77 years old. Very frugal, but wise enough to not use thread that is questionable. I remember my home economics teacher telling the class that cotton thread "dries out". She said to sprinkle some water on the spool, wrap it air tight (now we would use plastic bags) and store it in the freezer for a week or two. It rehydrates the thread, and it should be good as new. As for polyester threads, I agree with the strength test. If it breaks easily, use it to teach a younger person to sew!